Thanks for your query.Based on the facts that you have posted it appears that you have noticed colour of urine being pinkish after having frequent sex over a short period.
Normally after sexual intercourse small quantity of semen remains in the urethra
attached to urethral mucosa and it is most likely this semen gets mixed with urine when you pass urine after sex giving pink colour to your urine.
It is a natural phenomenon and nothing to worry about.
Ensure to drink more water before and after sexual intercourse .