Thats a lot of d3 to give him. It is recommended to only give it 2 times a month, give a multivitamin 2 times a month (both d3 and vitamins should be 2 weeks apart like you said you do with the multivitamins), and the calcium without d3 every feeding
A lot of people have figured out what works for them and have tweaked this a smidge...
What are your temps like? At the basking spot, and ambient
If you do not mind, would you be able to fill out the completed health form so we have a better understanding?