What I do with mine is to keep lightly pruning it when it's flowering and this seems to promote it into re-flowering all during the summer. I trim about 2 inches off the ends that have grown beyond the flowers (hope that makes sense)

Have you heavily pruned it or is yours very young? I find mine flower more as they mature.

I'd echo Drcs question - young shrub, or are you pruning it all the time? Because that plant is pretty small for a Weigela, they usually get 6 feet by 4 feet for some varieties, up to 12 feet by 8 feet for others. If you're cutting to keep it small, you never will have much flower on it.

It was here when we moved in and is pretty restricted in where it can go with a honeysuckle overhead and forsythia to one side. I trimmed back the the stems that were producing lots of leaves leaves a no flowers as I did last year to good effect. I just do enough to maintain a shape. I probably need to wait and see what happens next. We never saw a single flower for the first two years and didn't know it's name either!

Any cutting should be done during or immediately after flowering, then it should be left to grow on for flowers the following year - trouble is, you probably don't have room to let it do that.