Co-codamol or prescribed codeine... It's what my docs prescribed me when I had bad abdo pain related to a blood clot. For the constipation, if loads of fruit n veg fails then you can take fibre capsules. Fibre Sure are safe during pregnancy or you can take the Senokot drinks.
Are the cramps caused by trapped wind - I suffered very badly from about 16 weeks. Sip some ginger in warm water and try to get on all fours until the wind...ahem... passes . Also fennel tea is good for digestive problems.
Are you sitting down a lot in the day? I had a desk job and found that my system was getting sluggish and helping the wind to build up - try and get up and walk around if you can.