I feel your pain! When I try to overwinter hibiscus and other tender plants it can take months of summer weather before they decide to bloom. The problem is these tropical plants need warm nights sooner to be coaxed into reproduction.  A warm greenhouse in the spring is the  quickest way to get them to flower but lacking that try moving your potted hibiscus into your home in February or March so that it wakes up sooner. You will need a bright window or grow lights to get the plant to start making new leaves quicly. By April it will need fertilizer while still indoors but then in late May when all danger of frost is passed place the plant outdoors but in a warm and sheltered area as nights can still be cool. Use a liquid plant food for flowering plants such as Miracle Grow in May along with Osmocote slow release plant food in the soil. The liquid plant food will jump start the plant and encourage bud formation  and the Osmocote supplies slow but constant fertilizer over the summer. Warmth, water and lots of fertilizer is the way I was able to get my tender plants blooming sooner - but still it took until mid summer so don't expect miracles without a greenhouse. Your hibiscus looks lovely so it is worth the fussing. The blooms will be even sweeter after the wait. Keep growing, Marianne Binetti