Thanks for the query.
The possible cause for your spotting are:
-Bleeding during ovulation. Called mittelschmerz
-Inter-menstrual spotting due to hormonal
You continue your thyroid
And consult gynecologist once and discuss regarding your problem.
With her suggestion you can go for hormonal pills for few months, possibly which will correct this spotting.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429