All good points esp the one about my obvious lack of experience in this matter.I'm with Stubblejumper on this on. The pitch of the butt with regards to the sight plane has a major impact on recoil and forcing the gun upwards and not straight back. Could losing weight affect this, yes. The pitch is fit based on not only how thick your chest is, and its musculature, but also your mount. Do you stand straight up or get out over the gun? If you have lost weight especially in your chest area it could have impacted the pitch of your gun.
I could be wrong but based on your description i would put you in a relatively inexperienced shotgun shooting category. If there is someone at your club well versed in mounting a shotgun for skeet/5 stand (yes it is discipline and shotgun stock style specific) have them take a look at your mount and how the stock is interacting with you physically to see if they can improve things.
One of the most common mounting mistakes i see with inexperienced shooters is having a shotgun with sporting or hunting dimensions and standing straight up like they have a high rib & comb trap gun. If you are doing this and the butt pad is not 100% on your chest but a portion resides above your collar bone its a recipe for a cheek slap.
As for the adjustable cheek piece they do help eye alignment with the rib, but they wont help stop the gun recoiling upward into your cheek.
There is lots on YT that will help here. I watched a fellow last night that talked about proper gun mount and where that puts your head in relationship to the rib. I think there is a spot I need to look at as well. I was plowing the butt into my shoulder and pressing my head down onto the comb giving me a good look at the back of the receiver. He suggested positioning the head on the comb before the butt goes into place on the shoulder. I tried this a couple times last night and there was a difference.






















































