You have experienced and been diagnosed with benign ectopic beats. Your heart has been checked out and been found to be perfectly healthy. You have to believe this. On the other hand, you are clearly suffering from an anxiety disorder, which is perfectly understandable when you are hyper-aware of those odd heartbeats, medically insignificant though they are..
The important thing now for you is to find a therapist who can help you learn to comprehend that the sensations you are feeling are not dangerous to your body, even under the stress of a vaginal delivery.
Maybe more important: The idea is to have a healthy and happy baby and mom. There is nothing sacred or magical about a vaginal birth. There is some mild evidence that the pain of protracted labor might--maybe--increase the bonding between mother and child, but it's sketchy at best.
Talk over your fears with your doc, and if you are advised to get counseling in the next (very few) weeks, go for it.
I have had both a natural delivery and a C section (baby was big and I needed an ovarian cyst removing at the same time). The recovery from the C section was actually easier than the natural delivery where I had a cut and tear. I also have lots of pvcs, so I know how scary they are. I would do as Achillea suggests and work on the anxiety - there are lots of free resources on the web, like Anxiety Network, and free guided meditations to calm you, plus lots of cbt books on anxiety. Pvcs and pacs are very common, so I would be guided by your drs advice on them and your pregnancy. They would not risk a natural birth if they thought there was a risk, but on the other hand don't be afraid of a c section either. Best wishes.
I'm curious how your delivery went, and if your pvcs, pacs went away after delivery. I developed ventriculur tachycardia and pvcs during my recent pregnancy. Cardiologists insisted that I had a c section. Their thinking was that if I had arrythmia during labor, the baby might not get enough blood. The c section went well, but my heart went a little crazy after delivery. I had to be monitored during my hospital stay. My heart has since calmed down. I have had no tachycardia since returning home and my resting heart rate has been in the 60s-70s. I still experience pvcs. I am hoping they go away soon, but my cardiologist is sending me for another holter and a cardiac mri. I am hoping your delivery went smoothly, and your symptoms have subsided.