I had the same thing, and it was an infection! Nothing to worry about, just tell your doctor when you can and they'll give you treatment, and if it goes untreated it CAN cause preterm labor, so don't let it go on, so make sure you get checked! :]
I had exactly same thing...cramping, brown discharge.....EVERYTHING IS FINE! Brown is old blood and as long as its not pink or red, you are fine..cramping are not so good but ok too, I survived :) When cramping, try not to walk too much and do much activitiy and also, go on pelvic rest. My u/s showed that I had hematoma in my uterus but it was dissolved in two-three weeks, so it was fine as well!! DOn't stress out, its not good for the baby...pray for the best, relax and know that a lot of women have the same thing and then have healthy babies!!