What Are The Chances Of STD Transmission Through Oral Sex?

I visited a massage parlour 3 times. The first 2 times I received a handjob. The 2nd time I received a condom covered blowjob and SEX. Instantly after leaving the second time I couldn't believe what I just did. I had full on sex with a sex worker. I wore a condom, but I'm still really worried now. I mean, she said she'd been there for 2 years so there's no telling how many men she's been with. What are the odds I have contracted something life threatening. I'm guessing the odds of me getting a full clean std screening are pretty low after something like this. Should I get tested in a few weeks and then again in like 3 months? I messed up so bad.