What Is Istihadah
It should not stressful. If you misjudge and miss a prayer, it is not a sin. If you said a prayer and you find out that you were impure, even then it is not a sin. You may wish to educate yourself on this matter, but with God, every act in His obedience is worthy of Sawab. In your situation, you have to decide whether it is menstruation or not, or an occasional impurity, and follow the Shariah accordingly. You may take advice from your doctor.