Guitar coming untuned

you don't say what type of guitar, but here some possibilities for going sharp:

if it's an electric with floating trem, one of the strings losing tension will cause all other strings to go sharp. one string can lose tension for all the usual reasons: winding slippage on tuning peg, old or defective string, popping over nut or string guides during bending. when that one string loses its tension, the trem will strain back increasing the tension on the strings a bit until everything restabilizes -- than raises the pitch on all the other strings.

floating trems themselves can cause general tuning issues during normal playing, even if not actively used for bending. some simply are not very well designed. most will at some point need maintenance (polishing, lubrication) to ensure smooth, catch-free operation -- again, even if you don't use the trem (probably should block it in that case). for Strat, FR, Wilkenson, Ibanez floating-type trems, adding additional springs will increase tuning stability by stiffening up the trem action (higher spring constant).

the problem described above also happens to some extent on all steel string guitars, but can be especially bad if the truss rod is not really engaged (loosely adjusted or actually broken) and not really "supporting" the neck against string tension. without proper truss rod support, the neck is usually too flexible to be stable under full string tension. it will also be especially sensitive to environmental changes.

it is a gibson studio les paul and does not have a floating trem

then see my comments about the truss rod and neck. that guitar should be very stable if properly set up -- though temperature changes will affect it as any other guitar. also check for a loose nut.

I tune my guitar regularly and usually my strings become flat as i play, but lately all my strings have been sharp. I know that string slippage and stretching is normal, but cannot explain why my strings are tightening on me. Is this due to the changing of the seasons, or do i have a problem with my guitar?

How old are your strings? Old strings tend to go sharp because of all the crud and corrosion built up on them.

If you've had 'em on longer than 3-4 weeks, change 'em and see if the problem goes away.

How old are your strings? Old strings tend to go sharp because of all the crud and corrosion built up on them.

it's not obvious why this would be the case (expect flat due to increased mass). how does that work?

How old are your strings? Old strings tend to go sharp because of all the crud and corrosion built up on them.

it's not obvious why this would be the case (expect flat due to increased mass). how does that work?

Just what I've observed from my own experience . . .