Urgent: Can I take an Acetaminophen based menstrual relief for back pain?

Julia
I've searched all over the house and can't find any Tylenol or acetaminophen but I have managed to find a crap ton of off-brand Midol. I've read that Midol is ibuprofen based but this particular medicine I have on hand is acetaminophen based. It contains:
500mg of Acetaminophen
60mg of caffeine
15mg Pyrilamine maleate
I don't know what the last ingredient is but I know that both acetaminophen and caffeine are considered safe.
Today is my baby shower and I have so much to do before so I really don't have time to squeeze a store-run in.
I'm stressing out because yesterday I was lifting a bunch of heavy things and running a bunch of errands and now today I've woken up with a KILLER backache. It's a constant pinching feeling in my lower spine and I feel so stiff, it hurts to walk/bend/get up. I'm in DESPERATE need of some pain relief before the shower!!