Short-term rentals are not allowed for private properties and HDB flats.
Do note that the minimum rental period for HDB flats and condominiums are 6 months and 3 consecutive months respectively.
However, most landlords prefer signing a 1 or 2-year lease.
As such, it may be challenging to get them to agree for a period of 3 months. You may want to consider renting a serviced apartment.
Hope this answers your question.