Best ask a pharmacist - they're particularly good at recommending "OTC" over the counter medications. For high temperature, paracetamol (which is in Lemsip - always check so that you don't overdose) is good; for blocked up nose, there are lots of sprays and drops. Lemsip (and other cold remedies) are also available as tablets or capsules. However, one sachet of Lemsip only contains about a teaspoon of sugar, so you might consider that OK?