Cat headbutted me so hard I have a nosebleed

My cats have always been very affectionate but my male cat headbutts you in the face if he wants attention. First of all: I am extremely pregnant and he loves laying on my stomach which is very painful. Secondly he headbutted me so hard I got a nosebleed. He did this while I was already petting him. I say no and put him on the floor but he keeps doing it to me and everyone hes met more than twice. I just need to know how to get him to stop headbutting and walking on my stomach

Headbutting is his way of telling you he loves you, just a sign of affection.
Cats can sense the hormonal changes in pregnant women so he may be doing it more and giving you more affection because he knows you are very pregnant.
I have never been pregnant so I can't give you amazing advice... my only suggestion would be, position him beside you while you lay rather than on you? Or maybe just keep him away from you while you are laying down? (Which I know very pregnant women do a lot of  ) Make a point to spend some time with him every day but if you need to lay down, consider putting him in a room or closing yourself in one away from him. You love your kitty but you definitely do not want to risk harm to you or your baby by him laying on you so much. 

Best of luck and I hope you have a safe birth and healthy baby!