Talk to Urologist on Testis Pain

Hello, when I get sexually excited, after some time the pain starts from lower abdomen to left part of urinary bladder and goes down to the testicles. That pain discomforts me. I feel like testis became heavy. If the testicles feel any junk at that time it hurts a lot and I feel discomfort while walking. But if I take a sleep the pain goes off the next morning and I fee normal. Why is this happening? Is this a ser issue?