After my HSG I only spotted a little for a few hours. After my sonohystogram, however, I spotted for a week, then stopped for a couple days, then spotted heavier and darker, then had a full on period 2 weeks early. I think it screwed my hormones up. Maybe something similar happened to you. All you can do it wait it out, but if you have fertility procedures scheduled it'll mess with your timing. You'll have to consult with the doctor.