My cardio. believes the cause was scarlett fever as a child. As for myocarditis I have no idea about that. I'm not real clear on the PVC's question but if your asking if they are excessive yes they are according to my cardio.
Being concerned is not helpful, but yes, this is a serious condition. It's not nice to see anyone having such diseases, especially not young people (you're at my age).
Most important, is the cause of DCM found? Is it excess PVCs? Myocarditis?
You need to keep close contact with your cardiologist, and if you get worse (more shortness of breath, chest pain, dizziness) or if you get arrhythmias other than PVCs (sustained tachycardia) something should be done immediately.
It's possible to get this condition reversed, but a cause must be found and treated, the earlier the better.
Best of luck to you!