Baby unlatching and crying after 2-4 minutes

I need a little help and advice!

My 4.5 month old was breast feeding fine (with a shallow latch, but that wasn't preventing her from drinking) up until 2 days ago. Now, after 2-4 minutes, she unlatches, cries, and won't take either breast afterwards. She sucks her hands after, and is usually definitely hungry just over an hour later (she was going for 2+ hours, and drinking for 9-12 minutes up until 2 days back) it's worst in the late evening.

Because of all this, she seems to be drinking much less per day, and it's worrying me.

She takes about 4oz of formula with no problem; no crying, or fussing. She calms down afterwards.

Now, I was experiencing OALD up until about 2 weeks ago, but now I don't spring any leaks during the day, nor while I'm feeding her. I'd just assumed my supply was balancing itself now, but now I'm starting to worry my milk is drying up?

Am I missing something? I'm not eating anything different, I'm drinking a fennel and fenugreek tea, and there's good quality milk if I squeeze a bit out. I'm just at a loss, and the baby books don't seem to be giving me any answers!

Any advice? I don't want to switch over to formula full time, and we're going on holiday for 2 weeks on Saturday, and I was relying on breastfeeding for the convenience and hygiene purposes (we're in India; water can be unreliable here)

Help!