pregnancy symptoms an negatives?

okay so I have a 3 year old daugter and a 1 1/2 year old son... both born c section.. recently i have been having some pregnancy symptoms and alot of cramping an no period so i went to the doctor yesterdat an the pregnancy test was negative but i just barely missed my period so the doc says to come back in a week. he also made an appointment for an ultrasound in a week and if still no period then i am to come in for a repeat pregnancy test.. but i was wondering if i have an ultrasound this early would the doc br able to see anything? and can scarring from c sections cause infertility?