How do I get my tax situation corrected?

I worked as an independent contractor for a few years and (stupidly)did not pay/file my taxes during that time. I have been working as an actual employee for companies for the last 2 years and have had my taxes withheld. Unfortunately, due to my fear of reprisal for my earlier non-payment I have not been filing my taxes. In total I haven't filed for the last 4 years. I want to straighten my situation out but, I don't have any old records of how much I actually made in that time, only estimations in my head. Is there any source (other than my old employers) that I could find this information at? Or should I just go see a CPA or Tax Attorney with a bunch of estimations in my head? PLEASE HELP!