Cramping after sex ??

Is it normal to feel really really crampy in my lower stomach after having sex ?? I also have bad nausea and have been getting sick in the mornings since we last had sex about 4-5 days ago . This is the first time I have had this pain and this is also the first time he came inside of me . So could that be a reason?? Can anyone tell me y I'm experiencing all this and what it means ??