Possibly 'angioneurotic odema'. If persists do consult a doctor.Allergy and the cause likely to be food borne(eg-nuts) or medications.
Unexplained swelling of the lips and mouth without any predisposing disease is frequently caused by allergies. An allergic reaction can occur suddenly, even in a person with no previous history of allergy. This swelling is called angioedema. Diagnosis is by clinical examination and complete blood tests, electrolytes and renal function tests. Treatment is by antihistaminics and steroids.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.