If you do NOT get a good foundation in A&P, at best, you'll struggle with the material.
What may also be of help is getting a little drug guide or an EMS pocket guide. When you go on calls, if you have time, look up those meds you find and the guide will tell you what conditions/problems they're prescribed for. These pocket guides will NOT tell you how the drugs work, how they're cleared, how they're typically prescribed, and so on. They're NOT a PDR or NDR. They're not perfect by any means, and they're not comprehensive (I've seen meds prescribed that weren't listed in the guides.) It's a start... and you shouldn't stop learning about the meds.
Once you get into College, definitely take the A&P courses and a pharmacology course. You'll learn a LOT that you can use and later on down the educational road, it'll make things a LOT easier for you to understand.
I think you might be looking more for something like this (and they're often at your large box and medical bookstores):
I got that right off the Informed BLS guide preview page.
I happen to prefer their ALS version for this stuff as it's a bit more informative, but there's fewer drugs listed. Some of that stuff just won't make sense until you've had at least A&P under your belt, and after taking Pharmacology, it'll look, well, very simple.
