Do I have bed bugs?

I have been going to my grandmas house and she lives in a older house, its in the basement but has a little window that opens up to the outside. I live in an apartment upstairs in my building. I have a room that is all alone up there, the person who lives in the apartment above me lives alone. I have noticed that I have had bed bugs for a while. I am so paranoid that I am going to have to go out and buy new mattresses. I am afraid of bed bugs. I am not sure what to do. Please help me with what I should do.