Bleeding

Hi friends... im in 9th week now. I ve done all my pregnancy test including ultrasound, blood test and urine test then everything is normal.. the heart beat of baby is 159. but today morning i had a bleeding once and now there is little spotting and yesterday night i done a masturbation. Pls tell me why bleeding occurs and is masturbation cause bleeding or is ot sign of miscarriage.? Im really scared abt it.