I have had severe constipation due to GI symptoms from long Covid.

What does work for me:
Three doses of lactulose, one tbsp at night and two in the morning.
I take one amitiza with the lactulose when the constipation gets worse.

For the first 4-5 months after getting long Covid, I almost could not "go" at all! Mag. citrate didn't even help. I stopped eating because I couldn't have a bowel movement and lived on ensure (lost 45 pounds). But the lactulose (plus amitiza when needed) actually does work!! Wish I had known about the med combo sooner!!!!!