I have had a clear, sticky penile discharge occurring. it is usually light but can increase after an erection. i have had STD testing and all came back as negative. included Gonorrhea, chlamydia, tric, and HIV. i had both a blood and urine tests done. i had one round of Cipro for a possible UTI but that has not had any impact to stop this discharge. my urologist has just prescribed me a 100mg daily dose of doxycycline. should i have myself restested for STD's? if not an STD, what other scenarios could it be?