Hi,
Welcome to ehealthforum.
The symptom of increased frequency of urine after intercourse could signal an urine infection or urethritis which could result in spotting (or blood in urine).
Report your symptoms to your gynecologist, you might need to have a check done along with urine test to identify infection. If any infection is identified, get your partners also treated simultaneously to prevent re-infection. Avoid having unprotected intercourse while being on the treatment.
Take care.