Formula help!!!

My son just had his 6 month shots plus flu shot on Thursday and we also had to grab a different brand of formula that day because Walmart was sold out. He’s had a few runny poops but he just woke up from sleep SCREAMING a pain cry and he’s been scrunching his legs and tossing which makes me think belly pain . I’m thinking it’s from the new formula so I sent my husband out to get his original formula (Walmart is back in stock) what can I do to help his belly pain until he gets lined out On his original formula? I feel so bad. He’s back asleep now in my chest I just feel awful