That's vague. "Cough syrup" and "flu tablets" are for treatment of symptoms and pain, not for sleep.
Drink only warm liquids, stay warm, don't exceed daily intake of painkillers combined from all medications, try to keep the same wake/sleep schedule, ABSOLUTELY INCREASE PROTEIN INTAKE. Eat only warm foods. DO NOT GET DEHYDRATED. Make sure you're taking in adequate electrolytes like, potassium, magnesium, salt. Increase vitamin D, zinc and vitamin C intake while sick. Depriving body and brain of nutrients when battling an illness puts a body in a freakout mode and sleep will be difficult.
DayQuil or the like during the day (non-drowsy) and NyQuil or the like before sleep. Melatonin one hour before sleep might help.