Hi There -
I just started taking msm and got my period very early. I did a search online about this and it is apparently very common for this to happen. I believe this is actually a very good thing, tho initially it worried me a bit. I realize in retrospect that this is likely just a cleansing reaction. I dated a naturopath once who said that one function of menstruation is to help clean the woman's system of toxins. Many women were very upset with the suggestion that their monthly moon is associated with some kind of cleansing process rather than solely for procreation, but I think that this makes sense. It's probably one reason why women live longer than men. If you think about it, blood is an amazing cleanser when we are wounded in other areas - it helps flush things out out that are not needed. I personally believe that is why some women have very long and hard cycles - either because their diet is poor so their bodies are bleeding for longer in an attempt to clean it, or because they have some emotional stress or imprint that their body is trying to rid itself of (I am a massage therapist and have worked with many sexually abused women, and many many of them seem to have extremely heavy periods, sometimes lasting up to two weeks).
I have a good friend who decided to go on a fast prior to trying to conceive her child, and she said that one of the cleansing reactions of the juice fast was that she had a lot of spotting and passed a lot of clots. She then was able to conceive a very healthy baby. She wasn't using msm, but this points to the idea that fertility increases after women's wombs have been cleansed through a period of increased bleeding.
I found in other forums where women were commenting on msm's affects on their cycles saying that eventually, their cycles evened out, sometimes after passing many large dark clots. Some women who had had very long hard periods of 10-12 days said that after this cleansing stage, their periods went down to 2-3 days and they had fewer cramps.
Since msm is a blood thinner, I think that it makes sense that women with thick blood, and the attendant congestion that comes from that, would finally have an opportunity to release the stagnant blood and mucus inside them when they take msm. If msm cleans out the sytem on a cellular level, then it is actually a very good sign that the menstruation participates in this.
I also got a breakout initially from taking msm, but i know that it is just the toxins coming out of my body, and that this is necessary and will rebalance itself. Many people also get headaches initially, though msm is indicated for help with migraines (migraines are also a thick blood issue).
Hope that helps! This is just my opinion. I am about to try conceiving soon here too and I feel msm is the perfect way to clean out my system for this. I am not worried about its effects on fertility or on my cycle. I will keep you all in the loop as my experiment with this progresses.