Your symptoms point towards a stomach bug ? You have not mentioned how many times you passed loose stools.
Loose stools lead to weakness as alot of important nutrients are lost along with water which further leads to dehydration
Would advice you to take plenty of water along with atleast 2 sachets of pre-probiotics for a couple of days. If the symptoms continue then you would need to visit the doctor for further consultation.
Tending to a 3month old can be tiring I understand, but stomach cramps
is not to due that.