If 36 days pregnant when the stomach appeared vague pain, the most common clinical reasons are the following: 1, must first rule out the possibility of ectopic pregnancy, because this time through the ultrasound examination is difficult to find the gestational sac in the uterine cavity, so to rule out ectopic pregnancy, it is recommended to draw blood to check the blood HCG, if the value of the blood HCG every other day did not double up, highly suspected of ectopic pregnancy, it is recommended that it is best to hospitalization to give observation. 2, the fertilized egg bedding caused by a reaction, some people will have a vaguely uncomfortable feeling of the lower abdomen, and even vague pain. 2, the fertilized egg in the uterine cavity in the bed and caused by a reaction, some people will appear in the lower abdomen vaguely uncomfortable feeling, or even vague pain, through the clinical examination, if the blood HCG is still normal, you can be in the clinical dynamic observation, it is recommended to appropriate bed rest.