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?

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.
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.