Ragdoll,
How much are you using? Did you get the instruction sheet with your prescription and/or did your doctor show you exactly how to use it? You only use a pea-sized amount--literally. You put it on your left pointer finger. Then with your right finger dab it into the pea-sized amount and put it in the middle of your forehead. Dab again and put it on your left cheek, dab again for right cheek, and dab one last time for your chin.
Next, pat the dabs into your skin. There will be enough. What's left over, put on your nose, a little under your eyes and on your hands. Don't think you need more because you don't. It will only cause irritation.
Mixing it with serum would dilute it and make it less effective. Rather than doing that, I would suggest just going to every other night for a while. Everyone is going to get some flakies in the beginning, though. That is normal and will stop unless you're using too much.
It's definitely worth it! This is the single most effective product available. (And that's not just my opinion!) :o)