I have not received ANY letters yet. Yet is probably the operative word.
The IRS will not do anything without sending notices first. They will send a ridiculous number of warning letters. You might be completely off their radar. Do not volunteer for trouble by contacting them.
If you have the money for a Tax Accountant, then you can organize your info and get their opinion. I would absolutely avoid Tax Attorneys: you are not a tax cheat; you are a bad book-keeper.
Did your employer or anyone else report your info to the IRS?
I seem to owe these days, so I do file on time now.
However, when I use to get refunds, I never filed my taxes on time.
I even filed three years worth taxes at once after I received a bunch of letters from the IRS.
They just sent me my refunds, and that was the end of it.
It sounds like you will probably get money back, so there will be no penalties. I think your stressing over nothing. Get your taxes done and see where you stand.