My Husband 31 Years Old And Has Been Experiencing PAC

My husband 31 years old and has been experiencing PAC heart beats for the past 3 weeks. He has been to the doctor and had 2 EKG's and the only time it showed up was when we called an ambulance to our house. He has seen a cardiologist and been diagnosed with Hypertension and is taking metoprolol tartrate 25mg and buspirone HCL 10mg for his high anxiety. He had a complete blood panel done and everything came back great. He has recently changed his diet to a paleo based diet and stopped all caffeine. He has lost weight, which is bothering him because he's always been small but normally weighs between 165-170 and now he weighs 154.
He is very worried something is majorly wrong with him...
He has been on the medicine for close to two weeks and the PAC's, that were only happening 2 to 5 times a day, are now back and happening more frequently and it is really making him nervous.

Do you have any advise?