I would skip pruning your weigela this year and next spring so you don’t trim off the flower buds. That could be the problem since it flowers on old wood. Other than that, it sounds like you are doing everything right. They do best in full sun and yours are growing, so that means you are doing a good job watering. If you feel you need to fertilize, wait until spring and then give it one that has phosphorous and is low in nitrogen. Nitrogen grows leaves, phosphorous grows flowers.
Thanks for writing!