My 2 mth baby is cranky and not drinking milk. What shall I do?

She took her 2nd mth Vaccination and took Rotavirus medication 5 days ago. After Vaccination, she seems to have very irregular drinking pattern. We usually feed her every 2 to 2.5hrs, each feed is about 80 to 90ml. For the past 1 week. Baby started to be very cranky and refuse to drink milk and cry alot. Her interval between the feeding session can be as long as 4 to 5 hrs And she will drink about 40 to 50ml, sometimes 90ml sometimes 100ml.. very irregular. I am feeding her breastmilk from the bottle. I am so worried. What shall I do? Shall I go to the doctor?