Was this unprotected vaginal sex? That does open you up to a whole host of things. However, the day after sex is almost too early for anything to show up. Is it still there? Since you had unprotected sex, if this is an unknown person to you and you aren't aware of their std or HIV status, you'll need to test for HIV at 28 days with a 4th generation duo test. Low risk to have a one time unprotected exposure but still a risk. Other std's are normally only tested for if you develop symptoms. These red lumps are early to be a symptom of the sex the day after intercourse. If you are having sex frequently that is unprotected, remember to get regular std screenings.