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..... :-)
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!