I think tht most have it right, prolly fruit flies....
Also, remember that cleaning and sanitizing are 2 different processes. When you are finished brewing clean everything, by clean I mean remove all the residue, dirt, scum, break, and such, dry and store.
Before you brew wash and sanitize meaning, ensure that all your gear is clean, then apply an agent that will ensure that the micoscopic nasties are dead as well.
Hope your next brew goes better, dont give up, and dont dump before you taste....lol