The reason you are having trouble adding weight to the bar probably isn't your low test levels. It's probably a caloric deficiency. After all, women and children get stronger all of the time and they have much lower testosterone levels than adult men. Most bodybuilders will say to eat about 300 calories more than your maintenance load when you're "bulking" but I personally have to eat way more because of my fast metabolism. I'm guessing at 120lbs you have a fast metabolism too. The amount of food you can intake and properly digest isn't going to magically double over night. This is going to be a slow process. Additionally, you shouldn't resort to eating food with "cheap" calories like twinkies, soda, and fried mayonaise balls. You should try to eat good, healthy, whole foods as much as possible (chicken, rice, potatoes, steak, etc).