The symptoms (pain in the penis and balls and really bad pain in my anus) along with the fact that you had multiple partners indicates that you should be checked for STDs. Also, a homosexual act could have resulted in infection too.
The pain in the testicles could also be a simple case of orchitis, the pain in the anus could be due to infection and the pain in the penis can be a simple UTI as well.
You would need a complete STD panel done which includes both blood and urine tests specifically designed to diagnose a STD. Also, urine will be tested for a UTI.
Also, since you have pain in the testicles (balls), you would need an examination by a urologist to see if there is inflammation.
You are right that the doctor would examine your private parts but you have to overcome this embarrassment as the problem you have needs to be treated. If left untreated, this can have serious consequences. A confirmed diagnosis or treatment cannot be given over the internet. Hence, please consult a urologist as soon as possible.
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