Good pm! At 3 months, yup, normal na yan, most babies start discovering their fingers around that age, kaya minsan makikita mo sila nag-sipsip ng thumb or fingers randomly. Hindi pa talaga nila alam kung ano ginagawa nila, it's more of a reflex and exploration pa lang, so wala pang pattern kung saan exactly ang daliri. One of my mum friends said her baby was the same at 3 months, nag-start talaga ng purposeful thumb sucking around 4-5 months, so give it time lang. Just make sure the hands are clean kasi lahat papunta sa mouth haha, pero otherwise it's totally fine and part of development!