I'd possibly suspect lack of enough caloric intake. 2 primary things can contribute to this:
1. not enough food,
2. too warm of an environment.
#1 can be remedied easily, particularly once you get Juan feeding regularly. The easy part is using Juan as your food amount and/or prey item size calculator. You want to use the widest point as your measure, this is generally the middle of the snake. I typically go by 2 rules of thumb: 1) prey items should be
no bigger than 1.5x times the thickest point of the body and 2) you should see a slight feed bolus (bulge) at mid-body for 24-48 hours
after feeding. Many small snakes go through an awkward stage where feeding 2 pinkies is too little and feeding 1 fuzzie is too much. Bob Applegate (a once large-scale king and milk snake breeder) always told me multiple small meals more frequently was more healthy than 1 huge meal. His logic was that this kept the metabolism elevated, thus assumingly optimizing growth to get young snakes up to larger, more well nutritionally balanced prey.
#2 can be a combination of it and #1. Too warm of temps and in poikilothermic animals, such as reptiles, you cause the metabolism to be elevated, which results in the animal needing more caloric intake to sustain muscle and fat masses. Kept too warm and the body will burn through stored calories, resulting in weight loss if insufficient amount of food is consumed. I keep my corns around 85-87°F. The higher end (87°F) is merely due to my herp room maintaining day highs from March until Nov of about 85-88°F WITH the swamp cooler running. Come winter, the room will typically drop to no cooler than 73-74°F day or night.
It's hard to judge from your photo of Juan, but to me he looks like he'd possibly be able to be fed either 1 pinkie 2x per week, 2 pinkies every 4-5 days, OR 1 small fuzzie every 5-6 days; this is based upon his weight, prey item weight, and is known as the Munson Plan - something I'd never heard of until this forum. I feed similarly to the Munson Plan, but possibly a little more frequently.
I have a set schedule of 1 pinkie every Wed and Sat for my hatchlings and juvenile small snakes. I have 3 corns within similar size and weight of Juan, snake#1 gets 2 pinkies on Wed and a single on Sat, snake #2 get 2 pinkies on Wed & Sat, snake #3 gets a small fuzzie Wed & Sat. Snake #2 & #3 are similar in size, but snake #2 randomly started struggling with fuzzies (she regurgitated twice within a 2 week period) and was dialed back to pinkies yet she's larger in length and weight. I tend to feed heavily on my young snakes until they are large enough to take small mice (hoppers/weanlings). Once they are that large they get fed once a week.
That's the long, too much info response. The short answer, I'd get Juan feeding regularly on 1 pinkie every 4 days for about a month. Then I'd possibly move to something more frequent or more in-line with the
Munson Feed Plan Chart (<-- click for the chart)
