Im really scared

So i had an ultrasound at 11weeks 4days n the bean was good, measuring big n had a heartrate of 160. Im now 12weeks 2days n ive been feeling upper belly pain around n above my belly button, nauseous when i don't eat, soreish boobs still n emotionally sensitive. I used the doppler to check the heartrate to put me in a better mood n nothing. I thought i heard a little heartbeat but it was low n my own i believe. Im freaking out because whenever we used it before we could hear his strong heart beat right off the bat. I went to the beach yesterday n swam, wasnt out in the sun much other than while in the water, n i walked around the pier. Did that do something? Am i even pregnant still??