It is possible to be allergic to medication even antihypertensives but it is safer to speak to your doctor before considering stopping the medication.
You should continue the benadryl
and consider visiting your doctor is the weals do not resolve or worsen, you may need a short course of steroids.
Some of the signs of a severe allergic reaction
would be abdominal pain
, difficulty breathing
, difficulty swallowing, swelling of the face or tongue.
I hope this information is helpful to you