If an exterminator is available more or less weekly, as you indicate, you can't yet do anything: a landlord must be given a reasonable opportunity to treat a pest infestation after having been given notice of it, and if they start treating it within a reasonable time frame, then they are allowed to take some time or multiple exterminator visits to correct the situation--that is, the law accepts that eliminating pests can require multiple extermiantions, and so long as the landlord is getting to it in good order, the landlord is fulfilling his obligation and the tenant has no recourse. If an exterminator may be there in a week or so, the landlord is taking reasonable steps and doing what would be expected, and you have no right to do anything more. IF the landlord and its exterminator do not resolve the issue (or at least cause a marked improvement) in a few weeks, you may have the right then to withhold rent due to a habitability issue or consider the lease terminated by the habitability problem, but first, you must give the landlord a reasonable chance to deal with this, and in the law's eyes, "reasonable" is not "instantaneous."