4 yr son full adenoids&tonsils removed 3/18/15. snoring&breathing issues again.had few colds since sept.can adenoids grow back?nose membranes swollen?

Rarely do adenoids : regrow enough to cause symptoms of nasal obstruction. Nasal congestion & fever, signs of a viral illness, can cause his current symptoms, as can allergies. If he still snores when well, his ENT may perform nasopharyngoscopy to visualize the anatomy & mobility of his velopalatal muscle & the operative site & order a sleep study to rule out Obstructive Sleep Apnea. If concerned, call his ENT now.

Unfortunately, yes: Adenoids can grow back, your son most probably has seasonal allergies, started again in fall with weather changes and back-to-school season, affecting his upper and lower airways, and possibly airway hyper-responsiveness causing respiratory difficulties, check aaaai.org or acaai.org for an allergist in your area, wish you both wellness