I am so sorry to hear you are having so much trouble. This entire process seems so different for everyone, so it is scary thinking "Is this normal!??!" several times a day! The best position I have found to pass a BM is leaning way forward while on the toilet (like some have replied already). I received many helpful, different tips on how to position, but I think it really just comes down to each individual.
Also, I would 100% recommend pelvic floor physical therapy as well. I started in between surgeries this year, so have been attending for over 4 months now, and it has made an immense difference! There are things involved with muscles down there that I had no clue about!!!! My therapist has taught me proper ways to activate my pelvic floor muscles, what not to do when going to the bathroom and has helped me find so much relief when it comes to pain from straining/going incorrectly.
Hopefully you get everything figured out soon and you find the things that work best for you and your journey. All the best!