Okay, good question. So let’s just have a sideways look at what’s going on here:
There’s only a very thin gap between your vagina and your rectum, so when you fill your butt, it pushes everything even tighter. The key to it being more comfortable (it will ALWAYS have the potential to be quite ‘pinchy’) is the exact shape of your toys.
A butt plug is designed with a bulge so it stays in, but that also pushes it against your vagina. You’ll probably be much better off with two dildos (don’t mix them up) as they’ll not cause such a squash inside.
Just remember, anything going in your bottom MUST have a wide flange at the bottom so it can’t slip up and not come back out. The silicone dildo I recommend on my toys page is actually great for anal play, so maybe try that:
But any dildo that can go into a strap on harness will also have that wide base that’s so important.