Op you sound very very similar to me.
Post partum, I really really REALLY recommend someone called Better Body After Baby by Julie Baird (for all of you back pain ladies she’s on insta as ourfitfamilylife). She strengthens core through a lot of specific breathing exercises.
OP yes I had done yoga for years and even now if I go back to it I end up in pain again. It stretches you in a very particular way and for some people ultimately it just might not work. Do you get hip pain?
I had the spastic muscles too, so badly that by the time I sought help I was prescribed Valium to relax them (anti spasmodic as well as tranquilliser it seems!).
In my desperation (and with the yoga background) I turned to meditation - really recommend headspace) as there was some evidence it helped with allowing the muscles to ‘let go’. It really helped me, I’ll never forget one session (all lying on back on mat with knees bent) one huge muscle in hip area just finally unspasming and the relief was insane.
Body control or APPI pilates both good. Basically a lot of very good pilates teachers are also physiotherapists, which is perfect as they really understand anatomy. I have left pilates classes run by perfectly lovely exercise bunnies before because I realised they didn’t have the understanding of my issues and so kept insisting that I ‘should’ be able to do xyz.
Oh - I think that julie Baird has a prenatal programme too. I didn’t do it as only discovered her this year but worth a look.
Oh, and Epsom salt baths but that may be contra indicated by pregnancy?