Ah the myth of new windows.
OK... even though you are a renter, there is stuff you can do. But you have to identify where the air leaks are coming from. Example: my mother was sitting in my living room one day, and said, "wow, this spot where I'm sitting seems to be colder than the rest of the room" And you know what... she was right. There was... I kid you not... a ventilation opening in the foundation of the house. It looked like a window opening, but it was just... open. So the only thing between my feet and the outdoor air in that spot was an inch of floorboards. No wonder it was cold in that location!!
So. You need to walk around the house and figure out where the drafts are coming from. A professional can do this, or you can just walk around with an incense stick on a a cold day, and observe the smoke.
The big culprits:
-new windows won't help if they don't fit properly. Hold the incence stick up to the frame of the window where it meets the molding or wall. see if you get a lot of draft from *around* the window. If you are getting a lot of draft from around the window, it's a fit problem on the window. tell your landlord, if the windows are new, there may be some recourse in the installation agreement.
-doors. weather stripping and storm doors can help.
-attic. (you'll see the incense, and all your heat, rising through the attic door or hatch) you may not have insulation. If you don't have insulation in the attic, this is probably the single biggest reason why you are cold. Talk to your landlord... insulation is an improvement that doesn't cost a lot of money.
-fireplace. Is there a damper? is it closed? If you are still getting a lot of cold air, a big wad of insulation in the chimney can help. (just make sure *not* to start a fire with the insulation in place.)
-hole where a fireplace used to be... check for mystery cold spots in the walls. or pieces of wood or metal covering old chimney openings.
-cold rooms. Some rooms may be underbuilt: a porch that has been converted to a bedroom. A kitchen add-on that doesn't have insulation or foundation. Closing that room off with a door or insulated curtains, etc, and using a supplementary form of heat in that room as necessary can really help.
Check some of these things. If you can identify why your house is so cold, it may not be complex fix.