I keep building my stack only to lose it with a couple calls. I can't tell when my hand is good enough to call.

By learning how to put opponents on a range of hands. This is probably the most crucial skill required in poker, and you learn it from experience and observation.
Poker is a game of incomplete information. Since we can't see villains' actual hands, we have to assign a range they could have based on their overall tendencies, their position, and the betting action.
Some players rely heavily on mathematical probabilities when deciding whether to raise/call/fold. Others use feel/intuition, but even that is based on (subconscious) math.

Good advice for a beginner would be "When in doubt, FOLD", especially if you're currently finding yourself on a losing streak. Villains don't bluff much at low stakes. If they are betting strongly and (especially) if they raise, they have a strong hand.
Playing in the micros, you should adopt an ABC style. Bet when you think you have the best hand, call when the pot lays good odds to draw to an OESD or flush, and fold when villain appears to have you beat. You wouldn't be making a huge mistake if you folded every time you bet and got raised, as raises (especially on the turn and river) usually mean "I have a better hand than you".

More on hand-reading and ranges: http://archives1.twoplustwo.com/show...Number=8629256
Complete guide to beating the micros: http://forumserver.twoplustwo.com/78...micros-430637/

Don't call big bets unless you have a big hand.

Engrave this on your mind and you will save a load of money.

Post some of your big losing hands where you called so we can see whats up.

This is part of the picture, but your hand is never good enough to call in a vacuum. It's only good enough for a call vs. some villains and not vs. others.

typical mistakes are when you call a big pot when you have already raised and want to win it at all costs and you end up actually loosing everything

Post a couple of examples maybe?
Also, if its a cash game then theres always the opportunity to wait for a better spot, theres no need to make dodgey, marginal calls wen you have all day to wait for monsters.

Man, I should have engraved that on my mind at the beginning of this month!
Reading/studying actually made me call more, since it was not aimed at micros where plaay is generally transparent.

AK is not a big hand, Any paired broadway is not that good when an overcard on the table, dont get involved in big pots with marginal hands .

OP, you need to consider a number of factors, the best thing to do is post some big losing hands.

This is not correct, quite apart from the fact that sometimes we hold the nuts which is certainly good enough to call (or raise) in a vaccuum, we sometimes need to call against any* villain and deal with the coolers.

* Of course, we can construct a theoretical villain who we will fold any non-nut hand against.

AK not a big hand? lol. 4th best hand in poker imo

What you gotta realize is that AK is a very profitable hand for advanced players who have a solid grasp of both preflop and postflop play. For beginners this hand can be really troublesome and should be played fit/foldish.