Skin Load

Hi, so no matter how many times I try my skin won't load in Minecraft. I tried changing it and everything but nothing seemed to work for me. I go into the launcher and I change my skin but when when I enter an actual world my skin goes to the default Alex or Steve. Also the skin doesnt work in mod packs, but I use version 1.15.2, and 1.12.2 for those. When if came to affected versions it didn't show anything from that time so I thought to add it in here. Thank you!!