Is it normal to get hard or cum when trying on clothes at stores?

When I try on clothes in a store fitting room, I always seem to get hard, and depending on the clothes, I'll even get excited enough to cum. This happens even if I'm not trying on pants/shorts.

When I try on pants or shorts, I'm always hard. Sounds strange, but when I'm seriously trying to try pants on, you can't tell how they fit with a hard on.

I got to the point of jerking off when I get hard, to 'get it over with', but some times that doesn't seem to work, and I'm hard again. I even came in a pair of pants I was trying on, since they were snugger than normal. Its to the point now that I bring in an extra article of clothes, when I try clothes on, so I have something to cum into or wipe up with. when I just came, out in the open so to speak, I was getting cum on everything, from my old clothes to the mirrors, to myself, some times, making a mess. I'm afraid of wearing underware when trying on pants, as I don't want to mess my own shorts, and have to wear them the rest of the day with cum in them.

On vacation, the previous person left a nightie in there. Of course I came into that, but that didn't help matters. that when I got the idea of bring extras in. At a suit store, luckily there was some suits left in the stall, cause I couldn't bring extra in there.

I order clothes online now, but I still like to try most things on locally. I know this sounds bad, but I buy most clothes at full price, so I don't feel too guilty afterward.