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No. Ibuprofen or back pain cannnot affect your menstrual cycle in any way. The two are not related. Hope you feel better soon.
It does not sound like anything to worry about Midcycle spotting is common. Are you on a birth control pill.
No I dont think you need to do anything at all if it occurs with just this cycle unless you want or need birth control
It can be normal. If your pap is normal, your only concern would be a std such as chlamydia which can cause midcycle spotting.