When I tried streaming using OBS, it showed up perfectly fine on OBS, but when I went to my twitch channel, it was constantly loading and buffering. What exactly causes it to buffer so much? Could the amount of buffering vary between viewers?(possibly meaning it doesn't work when I view it, but might work when someone else views it.) Are there any ways to fix this if it's a problem?

It can have various reasons:

• Your Internet Connection isn't able to load the stream in your streamed quality. FIX: Lower the quality (Bitrate, Resolution, Framerate, ...)
• Your ISP somehow screwed something up which may lead to bad download-rate at that moment. FIX: Contact ISP if it happens more often.
• Twitch had some problems with their servers - Because of big events like GDQ/ESA, ESL, LCS, ...) or technical issues. FIX: Wait till Twitch fixes it or change Region/Server.
• Your PC can't handle that much at once which may lead your stream not to load properly. FIX: Kill unneeded processes, Stop other downloads, Upgrade PC

OBS has an estimator at what bitrate you could stream. https://obsproject.com/estimator (y) This should give you a bitrate at which you could try to stream without it having to buffer. Without partner i would recommend not higher then 2k bitrate streaming because of not having quality options.