I too can go for weeks without any, then have lots in an hour or even several in a minute. I used to actually get a lot more (hundreds a day) but not feel them, but now get less but feel them as a flip in my chest.
I have read several times that it is not significant whether you feel them or not and the number isn't that significant either. There are people on this forum who have recorded thousands of skips a day on monitors and still been told they are fine. I think you are just unfortunate in that you feel them and they (understandably) alarm you. Put it another way, if you couldn't feel them you wouldn't worry because your doctors say you are okay. I have been through massive anxiety because I found it hard to accept that my ectopics are benign. Try your best to accept the doctors reassurance and move on, it is very easy to get caught up in obsessing about your heart.
If you have a normal echo, EKG and stress test (the stress test does not always have to be done), you do not need to worry about the extra beats. I like to see what I am dealing with so I usually order a holter or event monitor. It is almost always premature ventricular or atrial contractions. I agree with your doctor that these are nothing to worry about, but I understand the symptoms are hard to ignore.
I hope this helps.
I can go for 6 months or longer and not feel any palpitations (notice I say feel as we all probably get these at least one PVC or PAC a day) then go for months being in agnoy so to speak. Doctors don't really know why this is, much like how a patient with arthritis can wake up and have an excellent day with almost no pain and also wake up and be in tremndous pain.