Can you untack a belly button from the muscle wall? I can't stand straight and I'm being pulled down/head over heels.

Perhaps too much skin was resected and you have not stretched back. Even though you may not want to hear this, try gaining some weight and then losing it after 2-3 months just to help stretch things back out to something more comfortable. Tissue will stretch.

A physical exam is imperative to diagnose what’s happening.
It sounds like stretching exercises may alleviate your issues. If not, surgery may be an option
Best wishes,
Dr. Taranow

To make an assessment on the outcome of a plastic surgery procedure we generally need to see proper before and after pictures. Based on what you described in the words only it sounds like you need to do some range of motion exercises. Consider asking for a referral to a physical therapist to get a baseline of your range of motion and setting goals for improving them. The best time to get range of motion after surgery is soon after the procedure. The longer you wait the more there’s going to be develop stiffness but range of motion can be increased at any time.
Best,
Mats Hagstrom, MD