Hi Afrindiemum,
The best advice I can give you is to contact a board certified lactation consultant (IBCLC) who can show you how to tell if your baby is getting breastmilk from you. She may do pre and post weights but this is not the most accurate way of knowing what's going on.
You can find an IBCLC here
www.iblce.org Just click on the "About IBLCE" button and the US and International registries pop up.
Best,