Re: I want to breastfeed but...
Have a well balanced diet. Also don't stress too much. The production of milk is a natural process and the supply is usually based on demand. Once your baby is born, lactation nurses at the hospital will guide you on how to breastfeed your child in the most effective way.
Sometimes, like Saadia said, the mother just doesn't produce enough milk for various reasons. In such cases, you have to supplement with formula. I had to do that with my second daughter. I used to nurse her then 2 hours later, give her formula, then alternate with breast milk.
Saadia as you know breastmilk is so easily digestable so there's no rule of thumb here as to how often should you feed. It's usually whenever you feel full or when the baby demands it. You body will set the clock. But formula fed babies usually feed every 2 hours in the first few weeks, then the quantity increases and so does the gap.