21month old baby not eating, has a slight temperature, slight cough, runny nose also hasnt pooped in 2 days?

Not to worry yet: Sounds like your child has a minor viral illness. Low grade temp, not eating, etc. This is where you be the parent and cuddle them through it. First, donworry about no poop. Not eating much, no poop made. Make sure drinking - that's the important thing. Minimum of 4 wet diapers in 24 hours to show is maintaining hydration. Give whatever fluids child wants. More important to keep hydrated!