Toddler allergy?

My 18 month old has had what I thought was a cold for about a week now. Little cough, runny nose, sneezing, trouble sleeping..also a tummy rash. Now she's had this rash once before, we were told it was probably viral so I figured this one is linked to the cld virus. But now I'm looking into it, I think maybe it's an allergy instead? Her mucus has been mostly clear, it was a little green for a day or so but running clear now... Shes has always been a little sneezy, had dark bags under her eyes, her eyes get red often. Then the rash... How can I tell the diff. Between a cold virus and allergies? How does an 18 month old get treated for allergies? Her dad has terrible allergies if that makes a difference, I don't know if it's genetic.

Just give her benadryl, if she gets better it's an allergy and if not is probably just a cold. But if it is, it seems like it's something she is constantly exposed to so I would look into an allergist to determine what she is allergic to.

Give her child Benedryl. If it clears up the symptom then it is allergies.

Thanks ladies I'll give it a go if this cold doesn't get back in the next couple of days.