Even if you didn't wash the underwear, bacteria like Gonorrhea or Chlamydia can only live outside the body for less than an hour. I'm probably even wrong on that, for it may be that it Gonorrhea and Chlamydia require intimate contact in order for the diseases to be transfered, and that they cannot be transfered once they are outside the body and on a surface such as underwear.
In any case, you really have nothing to worry about. I have heard of all kinds of cases of people contracting STDs, but never have I heard someone contracting an STD through clothes (except for crabs, and you definitely don't have that either).
Thank You so much. That relives me quite a lot.