I just went through a bout of constipation with my 6- month old due to us changing from liquid concentrate formula to powder. I have since learned that the powder is harder to digest so we're back to the liquid. In any event, her poos were rock hard and made her cry they hurt so bad to pass. I'm not sure that just straining and grunting would qualify as constipation, neither the frequency - she often skips a day or two when she's regular. Know also that formula fed infants don't poo as often as breastfed. If your lo is on solids try foods such as pears, peas, peaches, apricots, and diluted pear or apple juice. Those all worked great for us. She was back to normal within a day of eating those foods and going back to liquid formula. HTH.