Greetings Laur36,
From the symptoms you are describing it sounds like you may have a urinary tract infection. If not treated you can get very sick. The infection can turn into Pyelonephritis which means the infection has spread to your kidneys. The
pain you feel at the end of urination is likely a bladder spasm and the feeling like you have not emptied your bladder completely aka: keep having to go frequently and feeling like your bladder is heavy and full is another classic sign of urinary tract infection. This infection has many causes and sex is one of them. In short, urinary tract infection is caused by a bacteria. Wiping the "wrong way", (back to front instead of front to back) can be another culprit. It is important to get up and pee shortly after having sex which can sometimes help.
THIS PART IS IMPORTANT!!! Go to your doctor. If you don't have one go to your nearest Urgent Care Clinic. If you get a
fever or your symptoms worsen go to the Emergency Room!!!! This is something not to be messed with Laur36.
Shelly