No thats not too small to have a baby..
You need to drink water and your gonna need to eat healthy (if your pregnant) for your babies sake. If you dont, you rbaby wont get any nuritment and wont develop. In the case that you are pregnant, your going to need to force yourself to eat good food.
Its not bad to eat junk every once in awhile, but not on a regular basis. Hamburgers and french fries for lunch everyday wont give your baby the nuritiment he/she needs..