I'm the exact same way dude, I drink monster everyday and have pretty bad anxiety but have noticed that it does help a lot and improves my mood every single time. I've been drinking them everyday for about 4 years. Coffee improves my mood too but doesn't help with the anxiety as much as monster seems to. We're both odd cases when it comes to anxiety and caffeine so if you're like me, you won't build a resistance to it, at least not in the sense that it'll stop giving you the same affects. You may be able to drink more caffeine than the average person from tolerance but it shouldn't stop helping with the mood improvements and whatnot.
Have you noticed any kind of resistance or are you just worried about it?
Also.. I wouldn't take any drugs if you've recently drank caffeine. I made the mistake of drinking coffee a few hours after smoking meth all night and it triggered a racing heart that lasted all week. I drink my caffeine in the mornings/early afternoons and take anything else at night.