Call an exterminator. Depending on where you live, your landlord may be legally obligated to cover the extermination fees because it is expensive.

You will have to wash everything, bag everything and then leave it in bags for like 2 months to make sure they're all dead. It's the worst but make sure that you do it right. I'd recommend googling for bed bags/covers which can save your mattress so you don't have to throw it out. I threw out mine but then since I replaced it with an "adult bed", the kind you keep for 20 years, I invested in a 30 dollar bed bug proof cover which will protect it from bed bugs in the future since we still don't know how we got them.