While it should not hurt to pee after sex (and it is always recommend that you do pee after sex!), it does not automatically mean any one particular thing. Burning while peeing, after sex or at other times, can be caused by many things. For example, it may be because of vaginal dryness, friction, rough sexual activity causing tiny cuts, or even an allergy to latex condoms or other products you may be using.
However, burning while peeing may also be a sign of a UTI (urinary tract infection) or STI (sexually transmitted infection). We recommend you get tested for STIs. You can test for common STIs at home for free at violetproject.org/the-violet-kit, or visit your doctor for testing! UTI's are also common, and are easily treatable! So, while there is not necessarily one cause of burning while peeing, we recommend that you visit your doctor if it continues to burn when you pee.