Your risk is about as low as it can be for a person who has had unprotected sex with two partners- very, very low. As you point out HIV infection is rare in heterosexual men and women in North America. In addition, in the very unlikely situation that one of your partners has HIV, your risk of HIV per vaginal sex act is only 1 in 1000 exposures.
AS for your symptoms, the skin irregularity under your skin does not suggest HIV in any way (or any other STD for that matter). As far as what it might be, I cannot say and would advice you checking it out with a health care professional, perhaps a dermatologist. In doing so however, I would not worry at all about HIV.
Because you describe unprotected sex with 2 partners I would recommend that you qualify for periodic STD and HIV "screening" (testing in the absence of symptoms) because you have had multiple partners over a period of less than a year. As a matter of personal protection, we recommend annual testing for anyone who has had two or more sex partners in the past year (we consider this to be health maintenance- we also recommend you get your blood pressure and cholesterol checked regularly).
Hope this helps. EWH