About increased heart rate, particularly at night

I have been a bit anxious about my heart for the past 30 days or so. I went to a doctor of medicine and he said that its just gas and that I don't need to worry and that its getting worse due to my anxiety. I have had this slightly heavy feeling in my left chest for about 4 or so months and I used to have very slight issues whilst trying to take in a LONG breath but now that issue is less serious after consuming the medicine that he has prescribed for me, which included pramin 25 and indever. Now, the issue is at night, my heart suddenly begins to race(After dinner usually). Along with that I have had a stiff neck for the past 10 days or so which sometimes turns into a headache. Also , I have a throbbing feeling at the back of my head but it doesn't cause any pain. I am always thinking about my body and getting anxious. Also, I should mention that my blood pressure on the lower side currently and I have been having a lot of bed rest and am avoiding red meat and so.(Although after consuming the red meat my heart races too). I also had asthma problems earlier in my life but currently I don't have any issues and I have never had to take any inhalers.