I have fluid retention under my eyes after a serious allergic reaction last year. What treatment options do I have? (photo)

If it is truly fluid under the eyes you want to see your allergist to treat it.  If it is not fluid, but instead contour irregularities from fat positioning you may want to consider fillers.  They work by using volume to camouflage these concerns.  See an expert injector in your area to learn more.

For puffiness and sagging under the eyes, we often use Renuvion helium plasma radiofrequency energy to achieve incredible results and take years off of your appearance. Combining RF energy and cool helium plasma, the signs of aging (wrinkles, pigmentation, skin laxity) are improved in a ‘Nonsurgical Eyelid Lift.' The focused heating tightens and peels the upper layers of skin with extreme precision, leaving the surrounding area undamaged, smoothing and tightening the periorbital skin, and improving the overall skin quality around the eyes. It's an aggressive treatment, and the recovery time is longer than with other nonsurgical procedures, but the results can be life-changing. See an expert to determine if this is the best solution for you. Best, Dr. Emer

It would be nice to see photos of your lids before the allergic reaction of last year, in order to better assess the amount of fluid you are retaining.  Is that possible?
If there is truly significant fluid retention, then the skin likely has been distended for a long enough time that it has lost significant elasticity.  I am a strong believer in getting to root causes when trying to treat someone, and caring for root causes almost always results in nicer, more natural-looking results.  That said, you would benefit from procedures and products that increase the production of skin collagen and elasticity, and encourage drainage of the residual fluid.  Even a HydraFacial with Lymphatic Drainage would give a good improvement.  Using medical-grade skin care (products that contain retinoids, stem cell growth factors, and/or small molecule technology) can improve the results of any procedure you do, regardless if iit is invasive or not.  A laser skin resurfacing procedure (CO2 or Erbium) could help or radiofrequency with microneedling.  I would avoid hyaluronic acid fillers, as they will draw MORE fluid to the area.
Again, seeing your eyelids before the allergy reaction would be so very helpful in giving you sensible recommendations.