Set glue traps on the floor, the really sticky kind used for rats. Make sure you place them in a part of the floor where you won’t be likely to step in it, like under your bed or under furniture. By morning you should have some insect trapped on it. If you can’t identify the trapped bug from the many, many, MANY photos of bed bugs floating around the Web, or if you want a second opinion from a professional, stuff the insect(s) along with the trap (don’t try to touch the trap) into a large Ziploc bag and call 311 to find a Department of Health laboratory who can analyze the specimen and confirm whether the insect is a bed bug or not. I understand this is a free service, I’m not completely sure of that.

Good luck!