HELP !!!! House Fly Infestation

Well i usually see about 3 or 4 flys in my grow room and just kill them but today i went in there and there was around 50-75 flies having a fucking orgy on my plants they seem to have increased in numbers a couple days after i gave my plants their first water with molasses . I know that they dont do much harm if any to the plants but they are so annoying and just give me the hebby jeebies ...so today i picked up some raid fly killer and bombed on their asses showing no mercy lol ...and i got some sticky tape traps im going to hang after i get done typing this. So my question is i know flies start as maggots so im wondering do you think that they are in my soil because i hvent seen one maggot yet but they have to be coming from somewhere ...What can i do to get rid of them for good ?
Any help would be great , sorry about the punctuation im kinda in a rush typing this

take more that 2 days for most maggots to turn into flies.

you either have something dead nearby, or perhaps an old glass of milk.
or they are migrating in for the molassas id say u have a hole most likely