Dear jessy:When the bleeding is brisk and heavy the blood flows quickly out of the uterus and vagina. When the bleeding is scant and slower it has a much longer time to be exposed to the oxygen in the air. This exposure will turn the blood color brownish. Think about a piece of meat which has been exposed to air for a while. The outside will be dark brown/gray. Yet when you cut into the meat, and expose an area which has not been in contact with the air, the color will be red.
It is very common for women using birth control pills (BCPs) to have a "period" which looks more like dark motor oil sludge than bright red menstrual bleeding. The synthetic progesterone in BCPs creates a thinner lining inside the uterus. This creates a decreased amount of flow. This more scant flow will appear as a dark brown color, and thick consistency.
Should you be at risk for pregnancy, that should be ruled out first with a reliable pregnancy test.
Since you are not using hormonal forms of birth control, then the minimal amount of flow MIGHT represent a missed ovulation over the past month. The lack of usual menstrual cramps can also indicate a missed ovulation (as can an absence of the woman's usual PMS symptoms). With a missed ovulation just the top layer of the lining may be shed--causing a very light flow (or prolonged erratic bleeding. Missed ovulations are more common than one would suppose and can arise from ovarian cysts as well as medical problems and life stressors. Missed or erratic ovulations can make it more difficult to conceive.
More remotely, a small growth in the pituitary gland can both interfere with ovulations, and if the pituitary hormone (prolactin) is very elevated it can also shut down estrogen production. One needs adequate estrogen to grow a lining of the uterus which is thick enough to have something to shed.
jessy, if you have been trying to conceive for six months or more you might want to see a GYN. They can do testing for low thyroid, or elevated prolactin to see if these are the cause of your flow changes and delay in conceiving.
Yours,
Jane