You need to regain balance.
So you were a kind and caring person. Being kind and caring is great, but it's not the ideal tool for every social situation you'll ever come across. Those of us who want to be nice will find that it's not good when kindness is the only tool in your toolbox. Sometimes a firmer hand is needed.
The bullies, on the other hand, have the opposite problem. They're so used to throwing their weight about that they don't realise the benefits of being a bit kinder to those around them.
These two problems together = the bullying situation you find yourself in. The answer, as I said, is to regain balance. Fight back, in other words. Remember that the bullies are attacking somebody who's of approximately the same weight as them, and with fists of his own. So use the knowledge.
Just so long as you're sure you don't become a bully yourself, you should be fine. So go on, fight back. And let us here know how it panned out, I'd be keen to know. I was always taught never to retaliate and it just left me with an absolute cynicism of people (that persists in reduced form to this day), a delusion of superiority over all other people (which never did me any favours. 'not stooping to their level' indeed!), a mistrust of others and a big divide between me and my parents for telling me not to fight back in the first place.