I noticed that sometimes difficult to start urine but after starting my urine flow is fine. i was sexually active and i used many antibiotics. but i still have thin water discharge at the tip of penis especially in morning. all tests are negative?

This isn't an STD and not likely to have anything to do with your antibiotic treatment. It's a bladder or prostate problem that might get worse over time if not properly managed. See a urologist. Good luck.

There is a possibility that the watery discharge and initial difficulty may be due a tiny amount of urine left behind the opening after voiding due to a slight narrowing at or near the tip. Try gently squeezing gently after you think you have finishe voiding. If not better see a Urologist for cystoscopy. ( taking a look inside the passageway with a light. Good luck