Yes, absolutely call your doctor! Even if only for your peace of mind, you want to be sure you didn't do any damage. 6 weeks post op isn't very much. My doctor would yell at me if I did that and didn't call him!
I hope you're feeling a bit better. Like Michelle said, take it easy, use ice and/or heat, whichever works better for you, and try not to stress your back at all today.
Please let us know what the doctor says. And no more stools until you're completely healed!!!
Wishing you the best,