I feel like I don't eat enough & about losing weight?

Breakfast I usually eat a banana or a small bowl of cereal at 8 am. I eat lunch at 12-12:30, and it's usually a veggie burger, or a salad or a lot of strawberries and grapes. At 3, I'll usually eat string cheese. Then at 5:30 or 6, I'll eat salad, rice, veggies or a cheese quesadilla. (I'm a vegetarian) I also take vitamins everyday. I am content with my stomach by the end of the day, not hungry or full. It's about 800-1000 calories I'm in-taking. I'm trying to lose weight, I drink A LOT of water, and I run 3-5 miles every day and do about 50 sit ups and 30 push ups. I'm 178 pounds and I want to drop to 130 or 140, how long would that take? Also how much weight could I lose in a month or two? I'm a female btw.