Hello Betty,
I had SPD during my pregnancy and for about three years after my daughter was born. It was terrible, and you have my greatest sympathy.
The thing which has solved the problem for me has not just been using a treadmill (always at a 1.5% incline - it lessens the stress on the joints!) but combining that with going to a gym and strengthening my leg/bum/stomach/lower back muscles by working out with weights (mainly using the various machines on offer).
Frankly, I was rather sceptical when the muscle work was first suggested to me - and also a bit nervous, especially about doing exercises for the adductors and abductors. However, I started with low weights and lots of reps and I have seen massive improvement. Eight weeks on I can now even run again slowly, and certain movements which I had not been able to do for nearly four years (like taking my shoes off by pressing my heels together and siding my foot out of the shoe) I can now do again with no problem.
Frankly, it may well be that the weakness in the public bone is still there and now just "masked" by the better condition of the surrounding muscles. (But even that has given me a lot more quality of life!) My gym instructor swears this is not the case though. He says that the area was getting weaker and weaker through lack of exercise and that the improvement has stemmed from specifically exercising the connected muscles, thus subjecting the bone and cartiledge (sp?) to gentle stress and causing them to lay down fresh cells and regenerate (that's the science bit!)
I hope this is of some use to you. I have seen such an improvement. My public bone does still ache every now and again, but it's nothing compared to previously (and certainly no more than my other muscles complain after exercise - especially my stomach muscles!). If you do consider giving it a go though, do talk it though with your doctor/physio first and definitely find a gym with well-qualified, attentive instructors, ideally with some experience with the problem. You don't want to go from the frying pan to the fire!
Incidentally, as regards weight loss, I was still carrying about a stone from my pregnancy and have lost virtually all of it and dropped a dress size within eight weeks without dieting!
Best of luck!
TRQ