All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Dear Sister,
First of all, you should know that a woman may breast feed and yet have her menses. Indeed, many women menstruate while they are still breastfeeding. Therefore, the blood that you have noticed may be your monthly period, in which case, you should act according to that. However, if there is another reason which you did not mention to us and which makes you believe that the blood you have observed is not from your menses, then we ask you to send us the details so that we can issue an appropriate ruling about it.
As regards your question about whether or not you are obliged to wash your hair, then the answer is that you are obliged to do that if you perform an obligatory Ghusl (ritual bath) because of being in a state of sexual defilement or because of menses or postpartum bleeding. In all these three cases, you are obliged to wash your entire body and run your fingers through your hair on your head and on other parts of your body.
Allah knows best.