Back Muscles, Back Pain & Hip Pain (2.5 years postpartum)

[Yuvi]

I've been doing research on back & hip pain for 2 years now and still cannot find a re-assured answer to my problems.
I have never had backache until after the birth of our daughter (I was 29 then) - I felt quite fit even during my whole pregnancy and did moderate exercises throughout it. Then, during the delivery something went wrong and since that day I have been experiencing a bad backache. To make it worse, 8 months after the birth I started feeling this sharp aching pain in my left hip. I can walk only a short distance (1/5 - 1/4 of mile) and then the pain alleviates to such a level that I cannot make any single step more.
I used to walk miles and miles as I love walking and being active. We have a huge wonderful forest with a farm near our home but I cannot make even to get there! I'd love to take our 2.5-year old daughter to lots of places and pick her up like I used to do when she was a baby but...
I lived on strong uninflamatorry painkillers for good several months but they did affect my stomach so had to quit.
Doctors here in United Kingdom don't know what to suggest - X-rays and even MRI scans don't show anything wrong I was now put on the waiting list for physiotherapy and have to wait 18 weeks for my first appointment .
I've been doing exercises (pilates, yoga) for quite some time but they don't seem to be helping much...
3 months ago I went abroad to seek for other suggestions and saw a private doctor/surgeon. He suggested I only had to strenghten my back and pelvis muscles and everything would go back to their places so I will hopefully be 'normal' again...
I've been doing special exercise routine since I returned home but have no improvements as yet. Maybe I am doing something wrong and should I do the exercises if it hurts while I do them?
Just wanted to ask if anyone from you heard a similar story and is there anything else I can try ...
Didn't think it would come up such a long story - thank you for your time
Yuvi