Changes in seminal fluid compostion

Patient: Hi, I have some concerns about my semen quality and my fertility. I’m 28 years now.When I was younger it was a white colour and a lot stickier and had a high viscosity. About a year ago it became clear and very watery and not sticky at all. Also my girlfriend comments it doesn’t stick inside her vagina after sex, it just drops straight out.I spoke to my doctor and he said not to worry but he didn’t run any tests.I’ve recently been tested for HIV, HBV, HCV, HSV and Syphilis all were negative.I used to have a lot of unprotected sex with prostitutes and worried I might have caught a rare STD like HPV or similar.Any ideas what might be the cause of my change in seminal fluid quality and what tests I should request from my doctor to confirm my fertility ? Also any tips to get my fluid vicious and sticky again ?Thanks