I had similar problems starting around this age (my little girl's now 9 months) after a trip to Tennessee. I thought it was the time change, but apparently this is fairly common that a change in sleep - which is normal for the age and development anyway - can be traced back to a start at some event...a trip, a cold, whatever. From everyone I've talked to (doulas, sleep experts, pediatrician, etc.) it was the combination of two things: 1. She was hungry and needed more than breast milk (or I'm assuming formula in your case). She was ready for solid foods. and 2. She was starting teething.
Once I added in solid foods, it got a little better for a while. I avoided using Tylenol or Motrin for as long as possible. I still don't typically use it at all during the day and can get by with Hyland's homeopathic teething tablets. But after a few horrible AWFUL nights, I started giving her Motrin (a relatively small dose for her weight) before bed. That helped a lot.
I would also suggest that maybe your little one is ready for less sleep during the day? The sleep expert I talked to said 3.5 hours during the day is good for a ~6 month old. Now we're down to 3 hours at 9 months old.
Good luck!