Leopard gecko very sick please help!?

I'm in desperate need of help. I bought two baby geckos recently, one is a little bit older than the other, but they are both definitely babies. This is my first time owning geckos, but I feel that I am doing rather well. One of the babies I bought though is extremely skinny and small. The problem is, it was tiny to start with and now it seems to be on the verge of death. His tail does not have ANY fat and I can see his spine. Recently, the area behind his eyes have started to cave in. I noticed it not eating the first week so I tried to isolate it from the other to eat and it just doesn't act interested in food at all. What I have had to do is hand feed it live crickets. I hold the cricket from its back feet and move it in front of the baby gecko's face. Doing this it still takes a while for him to bite at it. Recently even trying to hand feed it, it turns away. I have also tried dead food (which is a no go for him) and mealworms (which he won't touch). I have found it sleeping in its water bowl, in the corners, or even the other gecko laying on top of him. The two geckos get along perfectly and are housed in a 10 gal tank. The temperature is usually between 85 and 90 during the day. And a pretty steady 75 at night. The humidity is usually around 40 but can vary. I mist the cage about three times a day and even spray some on their face and bodies to keep them hydrated. I also noticed his stomach having a very large triangle shape reddish mark but thinking he was just so skinny that I could see his organs, now I believe it could be the reason he's sick. Oh, and I've had him checked for parasites it's not that. He doesn't mind to be misted with water or held either, he actually seems to enjoy it. I know it's a lot to ask, but I also don't know exactly what type of gecko he is, well leopard obviously but he has stripes and everything but has a whitish tint overtop of it all and has two full red eyes, does anyone know that classification? Everyone I have talked to came to a dead end and didn't know what to do, that's why I'm posting here. He is so tiny it's sad I just want him better! I did so much research before I got them and thought I'd go with no problems but here I am. If you need more info just ask I'm willing to do anything to get this little guy better. Thanks so much in advance!