can't pass even soft stool without manual help, bloating

I am a 48 year old female, have had 2 children. This problem started about 3 months ago after taking 3 courses of antibiotics for a sinus infection. I don't know if that had anything to do with it or not. I cannot pass even diarrhea without using my finger to help it come out. I feel very bloated after I eat and pressure in my rectum. I have to drink a half a bottle of magnesium citrate before I go to bed so that I can poop the next morning. I can start to poop without my finger but then it stops coming out and have to insert my finger and sort of make circular motions and then it feels like my rectum goes up higher and expands and then the poop comes out. I have had a cat scan with contrast which was normal and a colonoscopy which was normal. Before this started I was eating foods with fiber and took a fiber supplement 2 times a day, so I don't think it is a fiber issue. I do have a partial drop in my bladder and some stress incontinence there.
Can anyone help me out? This is really driving me crazy! Also when I take the magnesium citrate my lower legs ache, what would cause that?