When I went to the washroom to relieve myself I saw a spot of blood in the toilet, which made me worried and I was not sure whether I was menstruating, Should I pray and complete my fast or not?.
It seems that a drop of blood is not menses, so it does not mean that you should stop praying and fasting.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked about a woman who had a few spots of blood in Ramadaan, and this continued throughout the month, when she was fasting; is her fast valid?
He replied: Yes, her fast is valid. These spots do not count as anything because they come from a vein. End quote.
Fataawa al-Mar’ah al-Muslimah (1/137).
He also said:
The general principle is that once a woman’s menses has ended and she has definitely seen the tuhr or white discharge that signals the end of menses or nifaas, anything that appears after that, whether it is a brownish or yellowish discharge or spots of blood or wetness, none of that is menses so she should not stop praying or fasting, and she is allowed to have intercourse with her husband, because it is not menses. End quote.
60 Su’aalan fi’l-Hayd.