Can a landlord increase your rent before the current contract ends?

Well, what's a contract versus a lease? A contract may not be a lease. If this is the case then the rent can be increased given proper notice (for example if you pay by the month then your landlord must give you notice of at least 30 days before the next rent is due). If the contract is actually a lease then the landlord normally cannot increase the rent until the lease expires, and must give you proper notice of such increase (at least 30 days before the next rent is due).