I had SPD in pregnancy and now have rheumatoid arthritis, which makes some aspects of parenting a real pain (literally and figuratively!) so you have my sympathy. My worst stage was with two little ones, potty training, and eight months pregnant on crutches, and my husband chose that month to go away on business.
Along with the empathy, some advice. Accept your condition, but do not let yourself get depressed about it. Take as much control as you can over it and don't rely on the doctors: I think doing lots of research, finding the balance of diet and exercise, and controlling my medication helps keep me sane and functioning. Do accept that there are, physically, some things you cannot do. Despite the advice not to yell at the kids but to go find them and talk to them, there's a lot of yelling up the stairs to mine because some days I simply cannot get upstairs to them. Get help with stuff, do not waste your physical energy on things other people can do for you (or that doesn't need to be done). And stop bending to potty train. If your little one is too young to follow instructions, wait til they are old enough to listen and do as you say so you don't have to bend down. If that means they aren't potty trained til they are 3, or 5 even, so be it! Having potty trained 3, including one with special needs/autism, I can confirm that all kids do it differently, and when they are ready, and there is no point pushing it til then, unless you are on some kind of insane competitive thing and have nothing better to do that do an endless load of laundry, stickers and big boy pants. Life's too short. Enjoy your kids, be the best parent you can, and don't let SPD get you down or stop you doing the fun stuff. And let the non-fun stuff go.
hth!