How to improve male fertility and sexual health?

It sounds like the sensitive skin on the lower part of your penis is causing you premature ejaculation (PE). This sensitivity could be due to various reasons, such as irritation from harsh soaps, tight clothing, or even an underlying skin condition. It's essential to keep the area clean and dry, wear loose-fitting clothing, and avoid harsh chemicals. I recommend consulting with a sexologist to rule out any infections or other issues contributing to the sensitivity. 

If your results were negative, then that is great news. Do not forget that it might take several weeks for the virus to be detected in tests. If you are still concerned, it would be prudent to go for testing again after a couple of months. 

It's common to feel concerned about the size of your penis, nevertheless be assured that size does not define your capacity for enjoyment of sex. Sometimes the issue of size may be due to stress or expectations that are not very realistic. Maintain a healthy lifestyle by eating well, working out, and dealing with stress. You can also train your pelvic floor muscles to be able to hold longer. You have to be aware that ultimate satisfaction is achieved through the connection and communication with your partner, not just through physical size.

You may be suffering from premature ejaculation. On the other hand, this could be realized with different factors such as, for example, stress, anxiety, and hormonal imbalance in your body. One of the methods I would suggest is to look for behavioral interventions like the start-stop method or the squeeze technique during sex. It is also possible to discuss with a doctor about the medications or therapy options which may be of help with your situation.