Is it uncommon to have mood swings near the end of your period?

Not rare: Hormonal changes during the menstrual cycle can easily affect mood. While there exist a number of typical patterns (pre-menstrual moodiness is one, observed since ancient times and all over the world) not everyone reacts the same way to these changes.

No: Classic pms mood swings tend to occur before the cycle but can occur during the cycle and even afterwards. The key is the timing and the onset. If it's consistently at the same time it probably is pms.