My second one went through similar episodes around that age too, and it was quite draining honestly. Since she started infant formula, it could be her digestive system adjusting to it, or sometimes a mild tummy upset that passes on its own within that week. That said, might be good to bring her to the PD just to rule out anything like lactose sensitivity or a mild infection, especially since it's happening in cycles. In the meantime, keep an eye on her nappy count and whether she seems uncomfortable or feverish, as those signs would tell you if it needs attention sooner.