Struggling during feeding

My girl is about 2 months. She has recently started struggling a lot during feeding this week, will suck from the bottle about 2-3 times before shaking her head side to side vigorously. So we will struggle with trying to force the teat in her mouth and with this method she will drink about 30-40ml before she stops sucking and falls off to sleep. She used to be able to drink 90-100ml per feed. She does this for both breast milk and formula feeds, and we have already tried teats from size 0-2. Any idea what might be the issue?