Pictures would be helpful, Maddie. Can we assume that you are trying to provide as close to full sun conditions as possible? These are outdoor plants and I'd be surprised if yours does well if kept inside on a permanent basis.

As far cold goes, no problem! Opuntia is extremely cold hardy, tolerating temperatures well below zero F.

I have a couple that are outside. I didn't even plant them in the ground when I first got them and they stayed in their pots outside through the winter. They will get a dark color and look shriveled during the winter months but when Spring comes they get revived. Both of my plants get yellow flowers on them.

What was said above, Eastern Pricky Pear (Opuntia humifusa) is a cold-hardy Opuntia from Zones 6b on up where it almost becomes weedy. You need to be sure of the species though, there are many, many different species of Opuntia (most not cold tolerant..., especially in the WET and HUMID East!) I have never grown the cold-hardy, eastern, coastal natives indoors.

I believe that Opuntia humifusa is hardy to at least zone 4.

Wow, did not know that as they're "native" range only goes to Cape Cod (Zone 7), on the coastal plain at least. I really like this species. I have other cacti but this is one of my favorites, it's like the bamboo of the cacti world, LOL. I have a another species of non-hardy Opuntia but it is wickedly barbed, and the hardy one is prickly enough!