We appreciate the sensitive nature of this question and wish you a healthy continuation of your pregnancy. Some first trimester bleeding is common, but if you haven't yet discussed this with your physician, we recommend that you do so at the earliest opportunity.
Not all browns are a niddah color. Some browns are acceptable on a hefsek taharah and stains of those shades do not invalidate the clean days. For example, a light brown with no hint of a reddish tint is not a niddah color. We recommend that you attempt a& hefsek taharah, in this case omitting the moch dachuk, and bring any questionable bedikot or stains for evaluation rather than assume the clean days have been invalidated. Please get back to us if you experience difficulty, as there may be room for some leniencies in that case.
BeSha'ah tovah!