how far along are you!? if under 3 months; more than likely its an onset of a miscarriage. if further than 3.5 months it could be any where from a weak cervice to a bacterial infection. either way call ob!!!!
Im not sure about spotting but if your just bleeding like I do in my pregnancys then you might have a hemmorage or something but if your pain is constant then its possible your missarying. What kind of pain are you having and where is it located?