Hi there Young lady.
It does appear to me that due to the 'mutual masturbation' you may have developed some sort of UTI that has led onto some sort of cystitis
(ascending infection affecting the bladder) & hence the discomfort you are experiencing.
All the medications you have been prescribed are all good..continue taking them.
In addition, may i suggest drinking some beer (alcoholic or not depending on your preferences) & following it up with lots of water. This will help flush out the infection & help void the bladder.
In addition a urinary alkalinser eg citralka taken 2-3 times/ day as per your pharmacists' instructions may help.
If you still have pain, get an abdominal USG (ultrasound
) done & go visit a surgeon.
No i dont think you have an STD!
Wish you continued good health! Cheers!!
Dr Praveen Rodrigues MD
Vikram Hospital, Bangalore, India