Sounds exactly like my daughter. She couldn't poop since she was 2 weeks old. We did the enimas for months and the stimulation, kayro syrup, prune juice, breast milk, different formulas, etc. Everything the doctor suggested, we tried and nothing worked.
What we did was put her on a pooping diet. I give her apple prune juice with water. (maybe you could mix this in her bottle) Also the only foods I feed her are:
veggies: green beans, sweet peas, sweet potatoes, spinach, corn
fruit: prunes, plums, apricots, pears, pumpkins
I did not know this, but applesauce is constipating, but apple juice is not. Once we started her on this diet, she's pooped everyday for 2 months!
On a side note, at 7 months, I really don't think prune jucie is hard on her. I was told to give it to her at 1 month old. You might also want to try less scoops of formula in the bottle and more water. When one is constipated, they need more water. Good luck!