If you cut out all dairy, you probably need to be taking a calcium supplement. But since you are nursing, please get your physician's advice on this. Generally a calcium supplement is not going to be harmful to the nursing child (calcium supplements are actually often given to new mothers to help replenish their body's nutrients which were depleted by the baby during pregancy) - but ANY medication or supplement should be under the advice of a physician if nursing
. I do think that if there is a correllation between cutting out all dairy and the PVCs getting worse that may be the cause of your problem.
Why does this happen after pregnancy? 
