Sounds like it may be overwatering damage. Are you able to show a picture? Nothing should need deep watering every day unless it's a bog plant in full sun.

Where I am, Weigela is a part sun plant - full sun until six would be way too much. It also sounds like too much fertilizer and too much water, all which would serve to stress the plant.

If you check plant encyclopedias, both online and in print, I think you will find most of them indicate weigela is tolerant of full sun to partial shade. Provided it is given sufficient water, any but the yellow/chartreuse or heavily variegated leafed forms should be able to tolerate full day sun (8+hours) without issue.

Burnt leaf tips typically indicates an excess of fertilizers; yellowing/dropping of interior foliage typically denotes overwatering. I'd cut back on both. FWIW, watering infrequently but quite slowly and deeply when you do is far better than frequent short bursts. And woody plants seldom ever need supplemental fertilizing and never when you first plant them.