I need some help from people with more knowledge and experience than myself. 

I want to preface by explaining that I have been on a weight loss journey for 3 years now, so I am having a difficult time figuring out how things are supposed to fit as I constantly change through sizes. 

So, my 13MWZ that I have been working on for 18 months are now fitting very loose and I went in to the store to try on new sizes. I have found something strange. I put on a 38 waist and the waistband fits well enough: not snug, not loose, but I can tell that if I use the same routine for wearing in, it will also be too loose in a matter of days/ weeks. So naturally, I tried on a 36 which fits very snug and causes a muffin top. I don't know if wearing these a few times will loosen the fabric enough to make it comfortable but I noticed huge difference when I reviewed the pictures. 

The size 36 feels more flattering in everywhere even though it is snug, but the size 38 looks awful in the crotch. No matter how much i adjust the pants, the crotch looks very baggy and like I'm hiding things under my pants. I then went home and tried on various jeans I own and while it is not as obvious, I noticed a similar situation as soon as I put on a belt and tightened it. My initial thought is that the fabric is cinching and causing the issue, but it seems bigger than that. Any thoughts or advice would be extremely helpful. 

Thanks!

Why do these 13mwz fit like this?