Hello,
Since you are sure that STDs can be ruled out, the only cause of such a pain can be urinary tract infections or prostatitis.
Mild prostatitis occur in all males from time to time - even in one as young as you are. They occur if the body's normal resistance to infections go down temporarily due to stress or due to illnesses like sore throat etc. They can also occur spontaneously. In most cases, they clear up by themselves in about 7 days.
If you take the Motrin twice daily for 5 days, it will work against both UTI and prostatitis. You also need to take a multivitamin multimineral supplement as wellas a vitamin C tablet 500mg to boost up your immunity.
I hope this helps.
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More than 20 years experence in active private practice. Wide knowledge base.