After pretty rough sex my insides usually feel slightly odd and ache the day after and my bladder is particularly sensitive. Is this something to be worried about or is it just because my partner is so well endowed?
Rugbylove, sex is not supposed to be rough. Your vagina and the vaginal entrance are very vulnerable and easy to tear. This is especially true of the vulnerable back side of your vaginal entrance which are pretty easy to damage. When you get aroused, your pain threshold also gets very high. So you will not feel the pain right then.
Even the most gentle sex cause micro tears. Rough sex will cause larger tears and chaffing.
Is he trying to hit your g-spot? That can most definitely affect your bladder as the g-spot is right by the bladder sphincter. If he is well endowed, he can also be hitting your cervix, which can cause anything from no pain, mild discomfort to debilitating pain and cramps.
With rough sex, you also need to keep your insides well lubed up. Friction is not fun so go for it with the personal lubricant and refresh it frequently.