Anybody know why? Example, I`m lvl 30 and the lvl 30 achievement isnt unlocked. Some unlocks and and some dont.

Have you been using the console? Doing so disables achievements for the rest of that session.

http://support.gamesas.com/eng/faqlist.asp?sid=185951101103071017172139&pid=400000953&pnm=Fallout%3A+New+Vegas&seid=400002568&pos=Windows+7&top=Achievements

I've noticed sometimes if Steam is doing server maintenance, credit for achievements can be delayed and will mysteriously show up later.