WHY wont my hair grow?

Okay so about 2 years ago I used to have loong long dark very healthy hair until one summer I decided I wanted to be blonde. So I made the mistake of doing it myself multiple times and I completely ruined my hair & had to cut it ALL off. My hair went from just past my boobs to above my shoulders. I then died my hair back dark so that it could start to grow back and be healthy again and I promised myself that I would never go back blonde (which after that experience, I NEVER will again) so it has now been 2 years and my hair is about 1cm longer than it was 2 years ago.. and I dont understand why it wont GROW!!!! well..it obvioulsy does grow because my roots appear very quickly but my ends just break off everytime my hair starts to grow so therefor it doesn't grow in length AT ALL :( My roots are extremely healthy, and once you get to the tips they dont seem very bad anymore but clearly they are still broken since they just break everytime. I have changed alot in my life, I work out regularly, I take multi-vtiamins everyday, Bioton (good for hair) fish oil supplements, I never brush my hair with a brush, always use my fingers or a wide toothed comb. I used morrocan Oil which is an amazing hair mask which has helped me out dramatically.. very expensive shampoo & conditioner. I have cut down straightening my hair to 1-2 times a week rather than 7 days a week like I used to, I get it trimmed about every 7 weeks. and I try my best to take good care of my hair since I want it to grow so bad. I dont suit short hair AT ALL so I have spent alot of money on buying hair extensions so I dont have to wear my hair short all the time...somebody please help me. I dont know what to do...every hair dresser ive talked to shows me a different shampoo & conditioner and swears by them that they will work..and they do..but my hair is still not growing in length. should I just shave my head? im beginning to think thats the only solution. HELP PLS!!!!!!!!!!!!!!