First of all, try to remove the sting if it is there. Apply ice pack locally. Apply Hydrocortisone cream or Calamine lotion. Take one Avil 25mg tablet and Ibuprofen 400 mg tablet.
Next Steps
You should consult a physician online at Practo if you are comfortable with this. But if you have lip swelling, breathlessness or choking sensation, then immediately rush to the local hospital.