Hi angela, this is my first post and I'd like to try to help you out.
My first question is: how long have you got left at high school? You said that you are 17, so I'm curious how much longer you have to stick it out. Fortunately, for me, my underarm HH developed a few years after I finished high school.
About the B.O - as I understand it, B.O. develops because of bacteria on the surface of the skin. Once the sweat hits your skin and evaporates, it carries the odour with it. So, the solution is to keep your armpits as clean as possible by using an antibacterial soap. I personally use a bar of Dettol soap and I find that it does the trick. In addition to this, you can use a deodorant (as I'm sure you are already using) just to make sure to mask any odour that does come through.
Now, to the social aspect of it all. I turned to my mother first and she, I think, was also a little flippant about it. There was nothing negative in her reaction, but she didn't take it as seriously as I wanted her to. But I realised that this was my fault because I played it down. Doing this is common, I think, because it is a way for you to try to deny the problem. Hell, heaps of people know about my HH (all my close friends and family) and I still play it down.
It's important that you make your mother aware of just how serious it is for you, regardless of how trivial she may think it. Tell her how much it is affecting you and your social life - let her know in ABSOLUTELY CLEAR AND POSITIVE terms just how much it can mess you around. By doing this, she should see that you are fairly stressed out and she will (probably) provide you with the support that you need. It's important to have this understanding from someone else, as it gives you a place to come to when you need to relieve the stress - you came here, after all.
As for your friend, I think if you really are very close, you should tell her about it. She will either understand, or she won't. But don't downplay it, whatever you do. Tell her, like you did your mother, just how much it is affecting you. Confider in her, and it might bring you closer. Is she that sort of person, do you think? Think of how you might feel if she was in your position. Perhaps you might like to tell her at the beginning of the school holidays, and by the end of it she should have a clear understanding of the sensitivity of the issue and is less likely to gossip amongst others or let something slip.
All that aside, here are some practical tips that you might already be aware of, but I'm going to tell you anyway
- Wear natural fibre clothing. I normally wear two shirts (I am a 24 yo male), both natural fibre. Doing this may be a bit hot in summer, but it allows for the undershirt to soak up any sweat. Sure, the undershirt might get a bit wet, but you have the peace of mind that your other shirt, the one on top, will stay mostly dry. And in the HH game, peace of mind can go a long way to keeping you dry.
- Apply antiperspirant at night, before going to bed. This ensures that the antiperspirant will be most effective. It will be absorbed best at this time and, in the morning, after using antibacterial soap, reapply it to dry skin. I only recently started applying it at night, and it does seem to make a slight difference, so it's worth doing.
- Seek treatment. You said that you were looking into this already, so that's good. I understand, being at school, that you might not have the time to search high and low for a magical cure, but you can do something. I have only recently started getting systematic about it. I have begun a spreadsheet and am tabulating data on the effectiveness of treatment methods. At the moment, I've only tried Botox (here in Australia, if it's for a medical condition, such as HH, it is free), and while that worked moderately well, it is inconvenient, painful and I don't like the idea of injecting a toxin into my body.
- Take note of what you are eating. Depending on what type of HH you have, it may be aggravated by hot and spicy foods.
One last thing. If you are worried about intimacy (and I'm not sure if you are) don't worry too much. I was very worried about it, met a girl, we got involved, we were intimate on the first date and somehow I didn't sweat! I was understandably nervous and thought that it might have just been luck, but the same thing happened the next time. I seem to sweat less around her - perhaps I have found my cure

We have been together for just over a week and a few days ago I told her of my HH. She said that she didn't care and that she just wanted to be with me.
So, to sum up all of this:
Tell your mother again, and make it clear BEYOND DOUBT the gravity of the situation.
Tell your friend after you have your mother's further support. Your friend will either understand or they won't, but not telling them is no solution to your (understandably) anti-social behaviour.
Explore treatment methods. There are many topical treatments available to buy online. Exploring this forum is a great way to start - you have come to the right place!
Take heart. You might feel stressed and alone at the moment with this ridiculous condition, but there are others (here on the forum) who can help you and, once you let more people in on it, you will have a strong support group. Your loved ones are probably confused by your behaviour, but they also want to help you. Let them in on what's going on in your life and you might find that you've already won half of the battle.
Good luck!