How much weight could i potentially lose?

Im a 21yo male. I weigh 187lbs and im 5'7'' .A month ago i switched from drinking 6-7 dr peppers a day to drinking nothing but water. I stopped eating fast food often. I try not to add table salt to anything, i also cut out little snacks. I eat about 400cal for breakfast and about 500-800 calories for dinner, i dont usually eat lunch but every once and awhile ill have 300cal for lunch.... Is this ok? also would eating lunch help my metabolism stay active until i eat dinner? How much weight could i potentially lose? Before i started all these changes, the highest number i seen on the scale was 198 and i usually weighed 196.xx. Is that good progress for a month?