If you deal with acid reflux & stopped drinking soda because of it 5 months ago, would starting to drink a couple glasses of soda a day again likely aggravate your reflux again soon after you've started drinking the soda again?

May, may not. Only way to tell is to re-start the soda and see if symptoms return. (Having experienced this once already, it is very possible symptoms may gradually return after drinking soda for a prolonged period - but only way to know is to try it)

Reflux may be aggravated by stretching the stomach and also by causing burping by ingesting gas (CO2) in the beverage. When you expel the gas, this can also bring stomach acid into the esophagus (reflux) causing local irritation.