I think i may have bed bugs?

ive been getting bites that look like small pimples some are individual some are 2 or 3 in one spot but i've been checking everywhere i washed my linens clothes my curtains ive checked in the cracks of my walls and my bed under the mattress checked the mattress cover i even had the exterminator come in and check for me and he couldn't find anything and he wont treat my room with any pesticides if there is no evidence(no fecal stains or anything like that), ive had this problem for almost a month and for me to have no evidence besides the bites ? the exterminator said he saw something on my mattress but it should have been on my sheets as well and it wasn't there should be some type of excrement on the sheets or even mattress cover is that odd could it be something else ? btw i do have a dog but i get her groomed every month so i don't think it could be fleas