I had a unilateral oophorectomy when i was four months pregnant. my first flow since is light & short, is it normal?

Yes, normal: This probably has less to due with the oopherectomy and more to do with the pregnancy. The first few periods after delivery are often erratic and can be heavier or lighter than "usual." typically these work themselves out with time.

Ovarian Cyst: Your periods will not be changed by have one ovary out. Your periods may be different after pregnancy compared to before.