Newborns to age 6 months almost always act like that are not satisfied. This is so that you will keep putting them to the breast so that they can build your milk supply.
The use of formula will sabbotage your breastmilk production and your supply problem will continue to worsen. The only way to know that your baby isn't getting enough is for him to not gain enough weight or for him to not have 7 wets in one day.
I think you should kick the formula if you want to be able to just use the breast. Kick it completely. Sometimes, at this age, your baby will be at your breasts, one after the other, for hours on end, which is called cluster feeding. Its frustrating, but normal...and doesn't mean that your baby is starving.
Some things that are said to build supply are oatmeal, beer, non-caffeinated root beer, fenugreek (you get it at an herb supply store, but you have to take 3 or 4 several times a day...if your body doesn't smell like maple syrup, then you're not taking enough), LOTS of water (drink about 60-80 ounces of water per day).