If you have symptoms of allergies I would just use a non-sedating antihistamine (speak with your pharmacist). Benadryl will dry your mouth out and give you a hangover.
I have dark under eye crescents with no fluid buildup. Unfortunately once you've had the issue for many years, the discoloration becomes next to impossible to treat.
Allergies can be subtle - post nasal drip, mild congestion etc. Seasonal allergies can produce the typical sneezing, watery eyes, and itchiness, but perinneal allergies often have symptoms that are less classic.
Oh, and consider a Neti pot.