It is normal, but I always told not to have sex during the first trimester. Granted I had a mc, before so this may have been part of the reason I had to wait. I am now 20 wks and I am still to afarid to have sex. My poor dh!!
If it last for more than an hour you might want to call your doctor.
Hope this helps!
Its perfectly normal to feel some cramping.... You can have a healthy sex realationship with your hubby.. It comes in handy too when your about ready to go into labor because the semen/sperm soften the cervix and make you dialate.. Don't worry about it, unless it get's too bad..... :-)