Having sexual relationships is something that can cause physical discomfort, that can last for weeks in some cases. If your sexual encounter was protected, there is not too much to worry about, but some STDs like syphilis, herpes and HPV can be transmitted even when condom is used.
Wait for a few more days, and if the discomfort sensation is still there, visit your doctor. It would also be interesting to test for those STDs i talked to you about. You should do it as follows:
-Herpes, 3 months after the encounter.
-Syphilis, 6 weeks after the encounter, and if your result is negative, repeat the test 3 months after the encounter, as there are people that take longer to show a positive result.