What's the point of getting a baseline in blood work when you are concerned that you might have contracted an std. also how soon after an encounter should you be getting this baseline?

If you have been at ongoing risk for STDs, baseline blood tests for syphilis and HIV may be wise; and if negative, to redo the tests later to see if they have become positive. Other blood tests usually aren't helpful (e.g. HSV, viral hepatitis, etc). Often it's more important to have test(s) for gonorrhea and chlamydia of exposed sites (e.g. genital or urine, sometimes throat or rectum).

Baseline cant be done after an 'encounter'. After an 'encounter' person ought to see an MD and let her decide when what tests need to be done