How do I fix my Bad Credit?

My credit sucks! I have been paying all my bills on time for the past 3 years! I even have 2 credit cards with low limits that I pay on time monthy! Whats hurting me is OLD Medical bills and 1 pervious credit card. I do not own a home .. I make payments on my car monthly.. What can I do to fix this? I would estimate $4000 if that has hurt my credit severly. Should I consider debt consolidation? What are legit companies? I need a fix so I can get ahead in my life! Any help???