Hi, no worries. Baby's birth weight is 3.5kg and now it's 7.2kg, it's normal for this age and weight gain is adequate. Regarding feeding till 6 months age exclusive breast feeding is enough for baby and there no need for formula feeding (if you are getting enough breast milk). With adequate breast feeding baby will go into sleep after feeds, will be active during awake, 6 to 8 times urination and usually 3 to 4 times pooping.
Next Steps
Adequate breast feeding and immunization as per schedule
Health Tips
Observe for weight gain, development and vaccination as per schedule.