24 weeks - impacted bowel??

I hate to be tmi, I truly do. But I have been fighting constipation tooth and nail through my whole pregnancy... been drinking water like a fish and taking colace, and also have been adding benefiber to my drinks a couple times a day (all ok'ed by my doctor). However, it doesn't all seem to be helping. Today I feel an urge to poop worse than I ever have and I'm in so much pain. But I sit down to poop and push and push and nothing comes out? Does this mean that I have impacted stool? Has anyone else dealt with this before and any advice you could give me on dealing with this and getting things moving quick and more often?!