Was what I did correct, or should I have prayed normally? And do I owe an expiation after the bleeding stopped and then returned, then stopped again, whereupon I performed ghusl, prayed, and my husband had intercourse with me?

If the spots appear outside the usual time of menstruation and are not accompanied by its pains and symptoms, they are not considered menses. In this case, the woman should sprinkle herself with water (perform istinjā' and ablution) and pray, and she should not perform ghusl unless she sees thick blood. This is because what she sees might be a "kick" from the kicks of Satan in the womb, as was narrated from Ali (may Allah be pleased with him). Accordingly, the prayers that were missed in this situation must be made up, and there is no expiation other than that, along with repentance and seeking forgiveness. It is permissible for the husband to have intercourse with his wife during that period as long as she does not see the blood known as menstrual blood.