Im at the Durlag's Tower and I can barely kill one party of monsters before I have to sleep and charge spells for healing. My party is lvl 2-3. Am I here too early?
Very much so.
Durlag's Tower is intended to be an optional, additional challenge for players. The underground sections of the tower in particular are, in my judgement, second only to the final battle in terms of difficulty.
Durlag's Tower is intended to be tackled towards the end of the game. The earliest you should be considering it is about the time you get access to the city of Baldur's Gate; if you want to be certain you're powerful enough, visit it just before the second plot-required trip to Baldur's Gate.
for a newbie, yes.
For a long term veteran, no.
level in BG1 (and to lesser degree, BG2) isn't really a big deal.
Most of your power comes from your gear, outside of mages, and even then they have options for low level play.
Once you know what you're doing and where to find good gear, you're pretty well free to go anywhere any time, that the game doesn't physically prevent you from doing so.
(BG2 is extremely rough under 8, due to enemies constantly spamming Death spell all over creation, but above 8, you can easily beat the game without gaining any further levels. Though Level drainers will be equivalent to death spells and need to be handled with utmost care).