oh gosh, daisy 123, thank you for posting!!
I can soo relate...
I actually believe in the LoA thing, like Aussie_Lad said, you can have many subconscious obstacles... and like Miss Buzz said, it's attitude+action most often that makes things happen!!
I've had things happen that may have been LoA in action... or just a funny way how the Universe works.. I don't know... I only know some things happened when I pictured a positive outcome and felt good about it... then let it go.. and sometimes forgot all about it, or was cool with either option happening (I had backup plan and such) 'if it's meant to happen, it will' or something like that..
relax and easygoing, or excited, like, oh wouldn't it be FUN if this happened??

(and when I was worrying and picturing the worst, or eaten up by self-doubt, they didn't... lol..)
There's an element to LoA to really let go and don't expect anything, and if it happens, it happens... this may be really hard to do sometimes, and maybe it's the hardest thing of all..
Also, a lot of this LoA talk may be just heavy marketing... A lot of people have written about similar stuff ages ago...
And even those kind of books say thoughts do not really determine who you are and what happens.. you determine the thoughts...
We are all also different.. A friend of mine says that things really only get better when she 'gives up', kinda the same as I wrote above, I think, to 'let go'.. Some people also do this naturally (picturing themselves in a new outfit or car, with a new person...)
Some may have too much negative self-talk and thoughts from before so that CBT/de-negativizing or other things like EFT/TAT/etc may be really helpful to counter those negative thoughts that can 'hamper' one and replace them with more constructive ones that actually allow one to change behavior and do better things... (Louise Hay and CBT describe this nicely)
So it's not just LoA, you can use it in combination with other things/approaches... I haven't watched The Secret mind you, it seemed hugely overblown at the time lol.. I watched Louise Hay's film on YouTube, it was quite interesting... Though it's important to go for the overall message, not obsess over every little individual thought.. some people even went as far as to 'blame' others for thinking negatively that got'em ill... This can be a danger.. Don't go there..
Our thoughts can be influenced by various things, like nutrition, environment, and toxics etc. And yes, even things that happen to us, people around us... So it's a combination of factors...
It's good to go for constructive thoughts and approaches - if LoA doesn't work for you, something else may be way better!!