Must I complete my fast if I experience intermittent bleeding after my period, and do I have to make up the days I fasted?

You made a mistake by fasting on the days you saw blood, because the default assumption is that the blood is menstrual as long as it occurs within the possible timeframe [of menstruation]. It is not considered irregular bleeding (istihadah) until it exceeds fifteen days.

You should have refrained from fasting during those days. Whenever the blood stopped, you were obliged to perform ghusl (ritual purification), pray, and fast. If the blood returned, you would revert to being in a state of menstruation, and so on, until the duration of the menstruation exceeds fifteen days. At that point, you would become a woman with istihadah (irregular bleeding).

You must make up the days you previously fasted while seeing blood. As for the two days you were pure, your fast was valid.