You must have pruned it incorrectly last year and cut out the new growth by mistake, or you removed the old flower heads which protect the new growth from frost in the winter. Leave well alone this winter and cover with a fleece or old net curtains when frosts are forecast
Mine have been wonderful this year because I pruned them really early. Last year I left it late and had no flowers. They need pruning really early before any new growth starts or not at all.