Do you have a reason to suspect your serotonin levels are messy? Drugs that mess with your serotonin/melatonin levels can definitely interfere with your dreaming. I doubt this is the case.

You probably just need to focus your intentions on dreaming. Make it a priority. Get a dream journal that is attractive to you and put it right next to your bed. Before going to sleep, open your dream journal and write today's date and a little message, such as, "I will remember my dreams tonight." Tell yourself this, and picture what it will be like to wake and remember your dream.