Sudden supply drop - am I drying up within a couple of days?! Panicking.

My daughter will be 7 months old in a few days. She's been exclusively breast fed her whole life. I've been sending 3x 4oz bottles to daycare since she started there in Sept. On Friday, her daycare teacher let me know that she thinks it's time to increase to 5 or 6 oz because she still seems hungry after eating. I was having no trouble with supply, and figured I'd just have to add an extra couple of sessions in to make up the difference. Instead, my supply suddenly tanked this past weekend. Not only am I not producing the extra milk, but now I'm struggling to even pump 10 oz per day. On Monday I pulled an emergency bag of frozen milk to make up an extra bottle. This morning I dropped off two 5 oz bottles (pumped yesterday) and then drove back to daycare at lunch to drop off the 3rd 5 oz bottle I pumped this morning. Since this morning, I've only been able to pump a total of 5 more ounces, so now I only have 1 bottle for daycare tomorrow. I plan on waking up every 2-3 hours overnight to pump, but I'll be lucky to end up with another 3 oz of pumped milk by the morning, and I really need at least 10. I don't know what to do. I'm afraid of not having enough milk at her 3am or 7am feeding because I've pumped so much. I don't have a freezer stash to dip into. I don't own formula. I can drop her off with the single bottle and then pump like crazy to be able to drop off a second bottle by lunch...but then there is no way I'm going to be able to pump and drop off a third bottle for the afternoon feed. Even if I was able to, I am robbing Peter to pay Paul, and it will eventually catch up with me in the next couple of days. I'm simply not keeping up with her demand. I'm so confused on why this happened so suddenly. On Friday all was fine and then within 2 days I'm no longer making enough milk to feed my baby. I've never used formula before, even with my son (who was breastfed until 1), but it seems I have no choice now. I don't own formula and I don't have any time to research anything, I just need to go out in the morning and buy something. It sounds silly, but I don't even know how to use formula (do I need special water or is tap ok? Does it come with a measuring spoon? Will she have any tummy trouble with a sudden switch? Should I take a day off work to keep her home tomorrow so she can try her first ever bottle of formula at home instead of just sending it to daycare? What if she doesn't like it? Do I need to keep it refrigerated once mixed in a bottle?)... Why is this happening?! Is this how it happens, over a few days you can just stop making milk? Is it because I got my period today? (It's my second period post-partum.) Is it because I have pink eye? Is it because I'm stressed over Christmas or something and just don't realize it? Is it because I suddenly tried harder to make more milk? What did I do wrong?! Is my breastfeeding journey over?