There are several situations that can result in early pregnancy spotting.
One is that you are having some implantation type of spotting. Sometimes at around 2 weeks or so after conception, when the egg implants in the uterus, you will have some spotting. Now, you are a little late for this, but everyone goes at their own pace, and I think that it is still a possibility in your situation.
Also, overdoing things can cause a little bleeding.
Having sex can cause slight bleeding, especially if your cervix is a little fragile.
And finally, of course a miscarriage will cause bleeding; but a whole lot more than you have so far described.
It is normal to have some spotting early on in pregnancy. With both of my pregnancies I experienced spotting. One for no reason; the other I guess was technically a miscarriage; when they did an ultrasound, they found one baby and one undeveloped sac that was sloughing off.
The pink tinge is from newer blood; the brown shows that the blood is old. Brown is much better than pink.
Oh, another thought is that a vaginal infection can sometimes cause enough irritation that you will experience some slight bleeding.
Also low progesterone levels will cause spotting and can eventually lead to miscarriage. If your levels are too low to maintain a pregnancy, you need to be supplemented with progesterone until about the fourth month, when the placenta is big enough to take of production.
Mild cramping is normal as the uterus grows. However, urinary tract infections, overdoing things, and miscarriage will cause cramping, as well.
Take it easy for a day, get 2000mg vit C in divided doses (meaning take 500mg four times a day), and drink a ton of fluids. If the bleeding remains (particularaly the pink spotting) or increases, or if the cramping doesn't resolve, I would definately contact a doc or, better yet, a midwife. It is probably nothing, but you don't want to blow something more serious off.
Take care, hope this helps!