The symptoms you reported (stomach discomfort, frequent urination, nausea, urge to vomit) are considered possible signs of pregnancy. Although they might be related to pregnancy, they are not enough to confirm it for sure. Other conditions that might cause unusual hormonal changes in the body might be responsible for the stomach discomfort and light brownish discharge.
Frequent urination is also present in urinary tract infections.
Therefore, you might want to visit your gynecologist for a physical examination and an ultrasound scan. A laboratory test for elevated Human choriogonadotropin (HCG) might be needed too.