Is there a blood test that can tell me what vaccinations i've had? (i simply don't recall/have access to my records going back far enough.) thanks.

Yes: Titres for MMR, chicken pox, DPT to name several.

Yes and no: There are many serum tests that can confirm you have antibodies to a variety of diseases and that those levels are high enough to be protective. They don't usually differentiate between natural disease and shots. Sometimes you can find shot evidence in baby books, school records or applications, many of which are kept for decades.