My baby who is 3 months and a week old used to sleep for 5 hours but for the past days she has been waking up every 2 hours for feeding she is exclusively breastfeeding. is this normal or should she start on formula?

Common in some: If you use a final feeding as babies transition to sleep, they will expect to be fed every time they alert & need more sleep. Babies like adults develop sleep rituals. You need feed at least 15-30 min before you let baby settle into sleep. Read to,talk to but do not hold as they settle. Over time baby will learn to self settle & can do so in the night.