Stop smoking pot and see if you're still feeling hazy. Lexapro made my hazy, and I feel a pressure in my head from it, so I'm going off it slowly (it hasn't worked, either). But I don't smoke pot; pot and anxiety usually don't go together, pot usually makes anxiety worse.
Ok...time to stop smoking pot. Not only will it drag you down, it is illegal, it can add to your anxiety big time. You probably don't want to mix the two and you can use this opportunity to get back on track and quit the illegal drugs.
As far as Lexapro goes, in my opinion with any SSRI, it does take some time to adjust to it. You said that you are starting to feel better; that is a good thing:). For me, it took a good month for a medication like Lexapro to kick in. Keep us posted!