Many conditions can cause vomiting. If you are currently sexually active, it is a good idea to be thinking about the possibility of your symptoms being related to pregnancy. However, without knowing more about other, related symptoms, it is difficult to say at this point.
First, yes, it is possible to be pregnant even if you just finished your period. In general, a woman can become pregnant and have what appears to be menstrual bleeding about 4 weeks later. This is called implantation bleeding, and occurs when the embryo is establishing a place on the inner wall of the uterus, called the endometrium--which is the same layer of the uterus that causes vaginal bleeding during your period. If you think you could be pregnant, then you should see your primary care doctor
for a pregnancy test.
If you are having any other symptoms, this could be helpful in determining the cause of your vomiting. Other symptoms, such as fever, chills, abdominal pain, back pain, diarrhea, or blood in your bowel movements could point toward other conditions like gallstones, gallbladder infection, gastroenteritis (e.g. stomach flu), or could even be a sign of diabetes in the right clinical setting. If you are having headaches or changes in vision along with the vomiting, this could be a sign of migraine headaches or increased pressure inside the head. Your primary care doctor can perform a neurological and abdominal exam to check whether there is reason to be concerned for any of these more serious causes of vomiting.
Also, if you are causing yourself to vomit by sticking your fingers down your throat, then this could be a sign of an eating disorder, which your primary care doctor can discuss with you, and might refer to you to another specialist such as a psychologist