Praise be to Allah.
These spots are not counted as menstrual blood and may be the result of physical exertion, sports activities or other than that for which you should consult your doctor. They do not indicate pregnancy as far as we know.
What you need to do is wash away the blood from your body and clothing and pray.
For further benefit, see the answer to question 38624.
Menstruation is a matter Allah has decreed for the daughters of Adam and during it the woman is not required to pray or fast. What a young girl experiences of uneasiness and emotions during menstruation is normal and affects most women, especially those who are younger.
A woman may dislike menstruation and be turned off by it since she needs to be careful of the blood, leave salah and not touch the Quran, however, those feelings do not harm her as long as she acknowledges the Shari’ah rulings and their wisdom; this is called a natural disliking. It is like a person disliking the use of cold water for wudhu or fighting, while accepting and submitting to the laws of Allah, as the Exalted says (what means): “Fighting has been enjoined upon you while it is hateful to you. But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not.” [2:216]
And similar to this is a woman’s dislike of having a co-wife while she believes in the permissibility of polygyny and does not object to the law of the Law-Giver and His wisdom.
So natural dislike towards something does not incur a sin, as long as the slave submits to the laws of Allah.
However, the more a slave’s Iman (faith) increases and the greater his understanding of the laws and wisdoms of the Shari’ah become, the more content they become and their hearts become accepting. They praise Allah for things which are pleasing as well as hardships; so the slave goes where he is ordered and stops where he is ordered and when hardships befall him, he comprehends what they contain of rewards and good and becomes calm and happy. This is not the case with everyone, and one who has not reached this level will not be held accountable for it.
We ask Allah to increase you in Iman (faith), knowledge and guidance.
And Allah knows best.