Ay, nakakaworry talaga kapag biglang nagbago ang pattern nila, pero honestly 4 poops a day at 4 months isn't unusual especially if mixed fed, a few of us tried combo feeding and aming babies din ganyan, every feed parang may output haha! Since it just started last week and wala pang other signs like fever, rashes, or sobrang watery stools, most likely okay lang siya, pero since you're concerned and malapit na naman ang Tuesday, definitely bring it up sa pedia just to be sure, they'll check if it's just a feeding adjustment or something else, para you'll have peace of mind din.