Breastfeeding Problem

Hi mommies, I am a Mother Nurture and M2 user. I also drink more than 5 liters of water everyday and eat oats in between pero bakit nagkakapoblema parin ako sa milk supply ko? I feed my now 4 months old son every 2 hours pero minsan di ko na nafefeel na napupuno o mabigat ang boobs ko. No leaking narin unlike before. Nafufrustrate na talaga ako. Btw I am a mom working in a financial industry. Considering our industry busy talaga everyday so nakakapag pump ako every 4 hours na and I could pump up to 5 to 7 oz sa 4 na oras na iyon. Please enlighten me what to do. I dont want to switch into formula milk kasi I know kaya ko pa i feed si baby hanggang kaya ko. Thank you.