When we have sex my partner is quite endowed but afterwhile my stomach kinda hurts and I have a little spot bleeding what is happening
Your partner is pushing or possibly penetrating your cervix. It would be common for this to cause some bleeding. Obviously if you do not like it stop! Try some other positions maybe from behind laying on your side, this will stop him from going in so far.
Yes I agree, it is probably just your partner being a little rough. This is not a problem, if you enjoy it, but if it hurts too much you should let him know.