The lack of fertilizer might be a problem, but the lack of strong light is also a possibility. Another real possibility is the variety. I have cane (angel wing) begonias that have never bloomed for me, and others that never seem to stop. So I'd suggest you try to identify yours--you could check pictures on the American Begonia Society web site and the Houston Astro branch linked to it and see if you can find it. Meantime, give it a light feeding, perhaps of a bloom booster fertilizer tho' not one of those with a really huge middle number, and perhaps a sunnier window if low light might be a contributing factor.

Which angelwing is it? I have a lot of different ones, and some of them flower faithfully and prolifically from spring until frost while others only really bloom once every 3 to 5 years. 'Looking Glass and 'Sophie Cecile' are extremely shy bloomers, for instance, but they make up for it by having some of the showiest leaves I've ever seen. Can you post a picture of your's?