why could this be happening???? it makes sense if a string goes flat, but sharp??
Makes plenty of sense. Sounds like the string is catching in the nut, so tension builds up this side of the nut whenever you bend a string at-all, and is not released. Make sure the nut slot is wide enough and use some graphite (pencil lead) in the slot to help it move over the nut more easily.
With the weather change this could be a truss rod issue.
check the nut and saddle as these are two areas where string pass over.. most notable is the nut, a poorly cut nut will catch and not allow the string to revert to zero.
When does it go out? When you use the trem? When you leave it for a day or two? The nut's the most common cause by a pretty wide margin but it's impossible to diagnose without details.
make sure you're intonated too
If the problem is with one or two strings, the next time you change strings, use the old string to slide, back and forth, several times through the respective nut slot. As a first step before getting a nut file set, this can sometimes help shape and smooth the nut for the size of the string and remove accumulated dust, grit, fibers that may accumulate in the slot.