Hi there, I wasn't diagnosed with the diastatis during pregnancy, but afterwards - it was then I realised that this is what I had all during my pregnancy.
I reckon I just considered it to be normal pain!! eeek - but it was increasingly sorer towards the end of my pregnancy, that and my bump was aching in agony over the tightness area of my belly button - and it was very very very itchy.
When I would get up from a laying down position my bump turned into a ridge down the middle and made a the strangest shape, and as my belly button had popped pretty early this was also a tell tale sign. Now I know better and if there's a next time I will be better prepared. People have now told me that my bump was absolutely massive from early on. I actually thought my stomach muscles were pretty good before I was pg, but I am not sure if this is a factor.
I ended up being induced at 42 weeks, mw tried a sweep on me at 39 weeks and she couldn't find my cervix - i told her i must not have one! I don't think that a sweep makes the contractions any more forceful as if it worked your body would be starting labour by itself. I ended up being induced (contractions started and waters broke) then they decided I had to be put on the syntocin drip - this did increase the intensity of the contractions but who knows? It could have been like that anyway, it was my first time so I can't compare.
Fastforward - I didn't get to the pushing stage I was taken for an emcs. But - if it's any consolation or advice I noted that once my waters had broke the tension on my tummy as a whole lessened, I felt a bit lighter.
Maybe wearing a splint would help, I am not sure about that over your bump though?
As you mentioned holding in the muscle has helped you a bit, keep on doing it and see how you feel. I think what she says is that you can actually push your baby out using this muscle and keep a relaxed pelvic floor? Not sure, but she also says when you do a poo to hold this muscle in, I have been doing that too and find it helps.
This should be under one of those topics of things they don't tell you before you get pregnant. After my CS I had incredible intense burning pain up my abdominal muscles, bearable with painkillers but not bearable when going upstairs. FWIW if this happens to you - remember you can actually use a tens machine on your stomach once the baby is out! I didn't know this and it actually took me over an hour to climb 13 stairs..... BUT much better after a few days of rest.
I don't know if any of this is helpful but please try not to worry about what will happen, you can't control that. Just concentrate on relaxing and remember to try and roll on your side out of bed. Keep us posted on how you get on, I'll be thinking of you xx