Male - mid-30s, monogamous relationship for 10+ years. Lately (past few months) during masturbation, I've had a swelling, uncomfortable feeling during masturbation. It's worth noting that this happens only during masturbation, not when I have an erection, nor throughout the day. No medical issues to speak of. Relatively healthy. Any idea what could cause something like this? Not sure if it's serious enough to warrant a trip to the urologist but also don't want to underplay something that may be more serious.