How long do dental fillings last, and can they cause problems?

I got some dental fillings for cavities 4-5 months ago. I think I felt them right after the operation but within maybe a couple of days I didn’t feel anything, and I don’t think I feel any difference now. I also periodically get pain where one of the fillings were – I’d feel some pain for a few days and then it disappears for a month or so. Does that mean I need to get it checked again and possibly refilled?