Since i can remember ive been using light martin strings on my little fender acoustic cutaway, they've been really reliable,coped well with my frequent low tunings, was easy to play and lasted ages.

recently i decided to have a change and brought some hybrid (same make) strings (bassy bass and even lighter high strings) they were nice at first, but the more i played them the more i realised i prefered my normal strings, and they didnt cope very well with any alternate tunings, the top strings got incredibly twangy, so i decided to go up a gauge again..

The strings i have on currently are martin mediums, and although they started out alright about a week and a half ago (when i put them on) now that ive just tuned my guitar to CGCGGC the top strings are incredibly twangy - what i'd expect from my banjo!
what id like to know is if it might be my guitar, i would have thought, if it had been fine with light strings, that it would be better with mediums, but its actually more twangy with them..

is it possible my guitar is more suited to lights rather then mediums.. or is it somethign that could have recently gone wrong? help and feedback would be much appreciated!
You need a custom set for that tuning, friend. I mean you don't have to, but yeah, string sets are designed for certain tensions and if you do a weird tuning that the string set wasn't meant for, it might act strangely. The light strings were probably just better for that tuning, so if those were fine, stick with them. Simple as that. You need to match string tension with tuning tension, so you can't just slap a set of whatever on there and expect to tune to whatever exotic system with no issues.

There are plenty of string tension calculators you can use online. Start here:
right, that makes some sense! thank you! thank you thank you, im glad its not my guitar its me/the strings!