It could be one of those "shy bloomers" such as Sophie Cecile or Cracklin' Rosie so nothing you are are doing is wrong. More light and fertilizer may help.

Thank you. I also have the plant close to an air conditioning and heating vent. Would this cause problems?

abkaus, I had a Million Kisses begonia that didn't bloom during the summer then I applied greensand to the top of the soil and it began blooming constantly for about three months in the autumn. I also have wax begonias (indoors) that were dying in the winter and after I applied Jobe's Organic All Purpose Granular Fertilizer on the soil they began blooming profusely and the leaves became larger too. I live in zone 5b and I water my begonias every two days. My begonias tolerate or thrive with any fertilizer I use.

I LET MINE STAY POT BOUND THEN LET YOUR BEGONIA GROW TO THE FULLNESS,I ALWAYS FERTILIZER EACH TIME I WATER,NEEDS TO STAY OPTIMNALLY HEALTHY AND SUNLIGHT. TRIMING THE PLANT DOWN SLOWS GROWTH FOR BUDDING AND TO MUCH NITROGEN CAN DO THE SAME. I USE A SIZED UP FOR A POT OR A HANGING KIND.DRYING OUT SOIL TOO MUCH CAN LEAD TO BARELY ANY FLOWERING PRODUCTION.