I live in an old building which construction is so old that it doesn't have necessary isolation layers to keep the heat out during the summer. Sometimes I think it's more hot inside than outside.
Are there any temporary solutions for keeping the heat out?
Man this summer was so hot! I don't know exactly what material would help in your situation, but you should definitely look adding a layer of some isolation to your walls.
I think you should consult a building engineer for advice on additional insulation materials for your house. Or search online for additional materials and instructions.
You could go ahead and get styrofoam insulation sheets to go on the insides of the walls. That would help temporarily until you could sheetrock the place.
Do whatever you can to keep the sun out during the summer and let it in during the colder months. Insulated drapes are a good step as they will also help keep the heat in during the winter nights but can be opened to take advantage of any sun coming in to warm it up.