With a normal heating bulb? What kind of heating bulb is it? There are those blue garden lights they sell in the garden section... Regardless, I think this is the reason your plant is tiny.

In Veg season, you need (light spectrum)5000-6500K which is also known as "cool blue" lighting or even "daylight". There are a number of options available. The cheapest way is either florescent tubes, or compact florescent lights. When you plug them in, they should look a little blue, as opposed to the other kind they sell "soft white", which is orange. If you go tubes, a simple 2 tube system would work for the time being, but you wont get the best results, as this is the cheapest method. If you go with the compact florescents, also called "CFL", get like 2-3 of them that say they are equivalent to 100W, but run 23W. If your just doing the one plant, you need not worry about the better options of lighting in horticulture like metal halide(mh) and high pressure sodium(hps).

On another note, your plant has been fighting for its life this whole time. It will take a while for it to get back on track when changing your lights, and there is a chance it wont. But if you want to see this guy through, be patient. The yellowing could be lack of light and the leaves are dying off, but it could also be a bunch of things.
Salvein211 Reviewed by Salvein211 on . My plant is so tiny? Hey I'm new to growing im not that big into it yet I just have a few questions. First off my plant is very small for being almost 2 months maybe 6 inches, and the bottom leaves are falling off and turning pale green almost yellow. Please help me Rating: 5