My guess is that it's nothing. Your own acknowledgment that you first noticed symptoms only after you learned there was reason for concern suggests anxiety more than anything else. On the other hand, your symptoms sound like they could be due to urethritis (urethral infection), the most common causes of which are nongonococcal urethritis (due to chlamydia or other bacteria) or gonorrhea (which sounds much less likely).
You are right to not necessarily trust your partner's statement she recently tested negative. However, most providerrs checking on women before or following abortion probably would have tested for chlamydia and gonorrhea.
Tell your symptoms and sexual exposure history to your health care provider and let him/her decide what tests to do. But most likely s/he will examine you and take urine or swab tests for gonorrhea, chlamydia, and tests for urethritis.
Good luck-- HHH, MD