what is wrong with my leopard gecko??!

Question
I really need some help with my leopard gecko. I have had him for three years and he has been in very good health the entire time up until about a few weeks ago. Out of no where he has stopped eating and takes him a very long time to shed. Also, he has big lumps on his left ram joint and left leg joint. He seems pretty weak and we have been trying to hold to crickets in front of him so he can grab them. He did very well with that but is not gaining any weight. He is actually losing weight especially in his tail. His tail is extremely skinny and i have been told that that tail size for leopard geckos if very important. Please help!
Thank you!
-Jessica

Answer
Hi Jessica,
It sounds like your leo is showing signs of having metabolic bone disease. Do you dust his crickets with a vitamin D calcium powder a few times a week prior to feeding them to him?  Also, do you provide a small dish of plain calcium in his tank? Also important is gut loading the insects for 48 hours prior to feeding them to your leo. Those gels they sell are not anything more than a water source for the insects.  The gut load needs to be a meal that is specific to the insects or you can use dark leafy greens, veggies, grains, etc. to gut load.  When insects are not properly fed, the leo does not get the needed nutrition.
Even though leos are nocturnal, I do recommend that they get some uvb light.  To do this, using a tube fluorescent light that produces UVB and UVA is needed.  Its important that it produces both.
Other causes of the lumps can be that he is getting too much calcium.  If you are dusting the insects at every feeding that can give him too much calcium.
On the shedding..are you providing a humid hide for him?  A humid hide is a very important part to their shedding process.
You are correct on the tail.  Leos store their fat in their tails, and when the tail starts to thin, it means there is some reason they are using up their fat supply.
I would make the needed changes(I am including a basic care sheet that I wrote so you can double check your care) and if those changes do not help, then a vet visit is needed to find out what is going on with your leo.
The lumps can also be abscesses which he will need to be seen by a vet ASAP so that proper treatment and medication can be given to prevent any further infection.