Where should I look for apartments to rent for period of 1-4 months? Are there any websites or facebook groups?

Try airbnb.

It would help if the OP gave a location and  affordable price range along with the style wanted: single room. one BR, ect.

 

Im looking for apartment that is 2-3 stations with mrt/bts to asok and no more then 20000bath per month. Preferably with BR.