I wouldn't say it is normal, but it is very possible. Yes you can still lactate after a miscarriage. Lactation is determined by hormones in the breast tissue, if those hormones are there you can lactate.
You can start to lactate during pregnancy because of the pregnancy hormones. This is preparing your body to be ready to breast feed once you give birth. You can lactate for a short while after miscarriage.
Every womans body is different. 4 months is a little earlier than most, but not unheard of. It depends how far into your pregnancy you are when a miscarriage occurs, lactating could occur if it's a late miscarriage.
It varies. No pregnancy or symptoms are exactly the same for every pregnant woman. Some women lactate during the first trimester, others don't until the second or third trimester.
