Are they small, black, and slow flying? Don't freak out and chop everything hah
Best yet, is to buy some Neem Meal (also called Neem Cake) from somewhere like neemresource.com and mixing in a few teaspoons per plant when planting, and sprinkling some around the top of the soil. This has kept all bugs out of my tent
Also, for immediate assistance, get some of those yellow sticky papers and hang em and/or place them down by the base of the plants. It'll catch some of the fliers, but the Neem will treat the larvae in the soil still