As a first step get bedbug-proof mattress covers. Also, you can prepare a spray of alcohol to kill on contact of you happen to see some.
They hide well. Exterminators look for signs of them rather than coming across the actual critters. The telltale signs are the bite patterns and spots on the mattress.
If you are in an apartment building they are likely coming from another apartment, and you cannot fix it alone. Otherwise, contact an exterminator. You might have to move out for s few days while they spray some poisons.
If you catch it early enough, you might only have to treat one room.
Much Hatzlacha