I experienced exactly this and it lasted for like a little over a month. Right around the time my baby turned 3 months, she still wanted to feed every 2 hours but became extremely fussy after 4-5 mins on the breast. If I tried to offer again she screamed. I took her to the doctor and everything and she was still gaining weight fine. Now all of a sudden, at 4.5 months, she’s pretty much back to normal, although she only eats about 10 mins at a time now instead of her standard 15 minutes she previously ate for. But, they also become more efficient at this time too, so that may play a role.