What Causes Pain While Lifting Objects After Hysterectomy?

I had an open abdominal hysterectomy (uterus and ovaries removed) 4 months ago. I am still experiencing pain if I lift heavy things (things over 15 lbs) and have seemed to have had a relapse in the amount of pain after having to lift my mother in law out of her wheelchair a few times in one day. I also transported a bunch of heavy instruments (drums and xylophones) by myself and I started doing planks around the same time, and that did not fare well with the lower abdominal pain. My BIGGEST concern is that I m a singer and my muscles feel weaker. As a result, it is now affecting my singing. It takes a lot of lower ab work to sing properly and to sing with power. Now I m having problems holding out phrases again like I did before the surgery, and I m having problems projecting my voice all of the way because my muscles aren t supporting me enough due to my recent, heavier lifting activities. How long does TOTAL healing usually take? My surgeon told me 6 weeks out that I could resume all heavy lifting and normal activities, but that is DEFINITELY not the case. Thank you in advance for your help!