I don't think it sounds like SPD (to me anyway!), but maybe an unstable pelvis, or just your hips out of alignment? It might turn into SPD, but SPD involves the symphsis pubis bones, which are in the front of the pelvis, your pubic bone 'joint'. As well as the ligaments and muscles surrounding your pelvis hips and possibly thighs. Usually the pain you get from SPD is in the front, in your pubic bone and/or hips. Some people can hear the lower back and hip joints clicking or popping in and out as they walk or change position (I can and can feel it grinding too-yuck!). You can also experience pain in the lower back, hips, groin, lower abdomen, and legs. It might make you walk with a waddling gait and have trouble climbing stairs, problems with lifting and lowering your legs, pain turning in bed or getting out of a car, pain when carrying out weight bearing activities, difficulties carrying out everyday activities, trouble pushing trolleys or prams and just general day to day things.