How do I find my tax return history... my new job is going to be doing a background check for the past 7 yrs and I have no clue what all jobs I did in the past

The obvious answer is to check your files - you do keep copies of tax returns and your old W2's, right? But I suspect you wouldn't be asking this question if it was that simple. So what you can do is order transcripts of your previous returns from the IRS. These aren't actual copies of your filings, but rather summary print outs with all relevant information. For info on how to do that see:
https://www.askmehelpdesk.com/taxes/how-get-copy-old-tax-return-irs-318020.html

Honestly, You sit down and think, I worked here, before that I worked there. And figure out, perhaps friends or family can help you

Contact the IRS and ask for Income Transcript for the years in question.