in sheer agony and feeling constantly full, heavy...

I had my son 4 months ago after a 4 hour back to back labour which resulted in a ventouse delivery due to his postion. I had a few stitches and felt ok, I assumed I would feel cramping, discomfort for a while.When my son was 2 months old I started having severe abdominal/pelvic cramps. I feel like my vagina is burning, heaviness in back passage, struggling to urinate (takes about 5 seconds to push it out) and feeling constantly full, heavy and pulling tugging type sensation, nausea, night sweats, aching joints, loss of appetite (lost all my baby weigh plus an extra stone which I could not afford to loose). I am in constant pain which at least once a day turns into sheer agony (worse than my late labour pains and I didn't have any drugs!) I've ended up in the emergency room 4 times for them to say see your GP.So I've had- blood tests, ultra sound scan, low vaginal swab, urine check all negative, had a lap which showed no endo but swollen uterus, mirena coil fitted. Any ideas?