Nightfall problem. Test i should go for?

I'm having nightfall from my puberty but usually the frequency is normal. Lately I have realised I get nightfalls only on the days when my body ks tired, like if I'm playing or exercising after a gap, I experience fatigue because of that and then the same night nightfall happens. There are no side effects of nightfall . I'm in a relationship and my sex life is fine as well. There are days I will experience NF continuously on 2 nights and sometimes only once in 2 weeks. But in last 12 days I've experienced NF 4 times and after when I tried to masturbate on the 14th day night, after cuming there is urge to pee and even after peeing I feel like that there is something left, I go pee again but only little comes, the feeling of peeing stays and also my penis shrunk after that. For the next 24 hours I had the same feeling and shrunken penis but now I'm feeling that penis is coming back to normal slowly and also the feeling is there but it jas decreased. Are there any test I should go for?