Sleep a lot, take vitamins immunity boosting supplements, take the proper cold meds (what you need depends on the type of cough/cold you have. Sometimes you need a decongestant, sometimes you need an expectorant, and so on), and, of course, stay hydrated. There’s no need to stop taking cold meds if they’re working, your body will do “what it needs to” just fine with medication. Cold meds don’t prolong a cold. The only symptom that might have an effect if you treat it is a low grade fever, but even then it doesn’t have a significant effect so it’s really not worth suffering over. So you can either look for some cough meds that don’t treat a fever (aka stuff without acetaminophen or ibuprofen in them), or you can just get the individual ingredients that are found in generic cold medicine which don’t target fevers and take them that way like guaifenesin or dextromethorphan or whatever one fits your particular cold. Or if you’re feverish and don’t want to feel uncomfortable you can just take cold meds that also target fevers and even if it does affect how long your sickness lasts, and tbh it probably won’t, then it likely won’t be to a degree that you’ll notice (honestly there’s debate on whether treating a fever can prolong an illness, but I’m trying to cover my bases). Most of the time when people think their cold meds made them sick longer what actually happened is that their meds suppressed their symptoms enough that they stopped resting and recuperating too soon and/or over-exerted themselves, and that’s what made them sick longer. Just make sure to continue to rest and stay hydrated properly for an appropriate amount of time and you won’t have that issue.