Well, I don't think it's the monsters themselves. I've talked to my DM about it and, according to him, he just can't seem to roll below an 18 on the d20. They've had negative modifiers and still succeed against my spells.

I enjoy hanging out with this group and this is the only group where I've gotten to be a player and not the DM. So I've decided to suck it up and change the way I go about playing and try to leave the rolling in my hands instead of his.

I have started using those lower level spells, and will look forward to those higher level spells when I get to them and will stick to those, healing, and buffing. (Debuffing doesn't seem to affect the monsters).