Is it okay for me to be mixing medicines for a cold?

It depends: You have to check the ingredients and make sure there is no duplication. Acetaminophen, for example, can appear in many cold remedies and too much Acetaminophen can be toxic to your liver. If you make sure you only have one source of pain and fever medication, one decongestant, one expectorant (for cough) and one antihistamine, then ok. To be sure you don't get confused, ask the pharmacist.