Recent research indicates that ghrelin plays an important role in the female reproductive cycle.
This is important to understand because MK-677, as well as all other GH secretagogues/peptides, are ghrelin mimetics. This means they act like ghrelin in the body, providing physiological effects similar to endogenously produced ghrelin. Ghrelin's primary role is the regulation of energy balance, which it accomplishes through the activation of its target receptor--the GHS-1 receptor. The activation of this receptor provides multiple, potential, beneficial effects for bodybuilders, such as the production of growth hormone and appetite stimulation. This is the main reason why bodybuilders use ghrelin mimetics such as MK-677.
However, ghrelin also affects the regulation of the hypothalamic-pituitary-ovarian axis through this same receptor (GHS-1), as GHS-1 is not only expressed directly in the ovaries, but participates in the regulation of multiple ovarian functions. This includes ovarian follicular and luteal cells, which help regulate the production of progesterone and estrogen. In this case, ghrelin has been shown to have an inhibitory effect on steroidogensis (the production or estradiol & progesterone) in luteal cells, which could account--at least in part--for the sporting you are experiencing.
Is this dangerous? No, not really, as even small deviations in female hormonal balance can cause several unwanted effects, including spotting. We see this occur naturally in many women as a result of the decrease in estrogen that precedes ovulation. This type of estrogen defiency induced spotting is usually light and intermitnet, although it may be prolonged in some.
Generally speaking, the effect that ghrelin mimetics have on the HPOA is so mild that they aren't considered (or classified) as hormonal inhibitors. This is why complaints of this nature are far and few between (this is the first time I've heard of this ) and we still can't disount the possibility that your spotting may not even be due to MK-677, but to other factors, either in full or in part. Regardless, for those who are teetering on the edge, even minor interference in this area may be enough to push one into the realm of unwanted effects.
Personally, I find it hard to believe that MK-677 is the cause..because if it was, it would likely be caused by a disturbance in the estrogen to progesterone ratio, which could be successfully treated through the administration of additional estrogen. Given your birth control intake, low estrogen seems very unlikely. I can find no other mechanism through which MK-677 might induce spotting...and combined with the fact that you are currently taking extra estrogen, as well as the fact that I have never seen this reported as a side effect (either anecdotally or in the literature), it seems unlikely for MK-677 to be the cause.
However, the only way to know for sure is to go off and see if it stops. Then, go back on after it has stopped and see if the problem resumes. If you repeat this ON/OFF approach 2-3 times and the pattern repeats itself in the same manner every single time, then it has likely been caused (or at the minimum, exaccerbated) by the MK-677. It is important that you run through this at least twice...because you could easily come away with false conclusions if you only do this once. After all, if the problem happens to go away on its own at or around the same time that you stop the MK, it would be easy to assume that the MK-677 was the cause, when in reality it may have just gone away on its own. This situation is akin to the uninformed beginner who starts using PEDs and automatically assumes that anything he experiences outside of the ordinary is due to the effects of the drug.