Your plant could just be in shock from transplanting it. I would wait another couple of months and see if it puts out any new leaves. It might also be getting too much water I would look to see if your soil is wet all the time. and most of the time when you plant new shrubs or trees you don't want to enrich the soil with potting mix or any other kind it can be it can cause the plant to become root bound in the in enrich soil always use native soil. I don't know if that will help you any.
But good luck with your new weigela.
