Changing String Elasticity Issue

[Omega]

I'm curious if anybody has had the same problem as me. Basically, sometimes when I pick up my electric, 7-string guitar and play it, the strings are very elastic and easy to bend, which is what I like. However, at other times when I pick up my guitar to play, the string are very tight and difficult to play. This happens with all brands of strings and seems to happen at random. I have a floyd trem, as an FYI and the body is ash.

Has anybody had this experience or can anybody offer an explanation? Could it be the changing weather temperature and humidity levels?

I just want to ensure this problem isn't a set up issue.

Thanks.