4 weeks and wanting more than 2.5 oz!!! HELP?

My son just turned 4 weeks and i have been giving him 4 oz for about a week now. After he is feed, burped, changed and whatever else he needs he still acts hungry! Even if i give him the pacifier he crys like he doesn't want it....should i add a little cereal to it? I had to do that with my other son bc milk alone wasn't working...what should i do?