Yes, I also have this issue. I think a lot of WLS patients go through this. As mentioned by a previous person, I like to take pictures throughout my journey and create side by side with them to prove to myself that I am in fact smaller. This is one of my best suggestions. I also recommend measuring yourself (hips, thighs, arms, waist, ect) to see the difference in measurements. Sometimes when I look at down at my thighs, it seems like they are still the same but when I look in the mirror, I can see they are smaller.
I too am very disappointed that I cannot try on clothes in the store at this time. I wanted to buy a few things for my birthday since I have not bought any new clothes since surgery (most of my stuff is too big). However, most places are not accepting returns in my area, so I didn't want to be stuck with something.