You said..."do you think the antibiotic given at the vet today might jump start that, if it's a possible infection? His grip still remains VERY strong and he is getting around well on the dirt. When he attempts to climb, he can. He just can't hold on for too long"...I was thinking that actually...but it won't likely work if it is an infection. Chameleon pus is like cottage cheese and antibiotics can't really get at it to clear it up. It usually needs to be cleaned out too.
You said..."I am currently having to force feed him. Any tips or recommendations on that?"...this should be a last resort. If he's not eating because his digestion is slow, he might not feel hungry. If they are spitting it out there's no point IMHO. Remember I'm not a vet and I can't be sure.
You said..."Today when I went to the vet, they gave him liquid metronidazole 50mg (1 mL) and invermectin (an antiobiotic and meds to treat parasites). Will this negatively effect anything if I go tomorrow and ask for treatment for mbd? They shouldn't counteract, right?"... I don't think calcium would affect anything but the vet should know if any of them interact....even if s/he's not a chameleon vet.