This exact same thing happened to me when I started with the Omega-3 pills. I wasn't really constipated, but didn't go to the can more than maybe once every 7 days. When I did go, it was more like puking, but the other way. Not very pleasant at all.
When I quit taking the fish oil I "normalized" immediately.
So my tip is to lay off the Omega-3 for a week and see what happens.