this is very hard! :D i relate, slightly. my son is 21 months old and theres just sometimes he needs me to hold him, no exceptions.
theres nothing wrong with putting your son into a sling again. on your back would probably be fine so hes not "in the way"
i understand though, that he might be heavy... i used the moby wrap and at all weights it has been a VERY comfortable way to hold onto my son! :D
i would just make sure that you can be as responsive as you can and understanding that this is just a hard time for him. rule out any teething, medical issues just in case, maybe even lay down with him before bed, give an extra story or two.
just keep listening to yuor instincts, they are never wrong. how you deal with this little step back determines how your son takes the next 2 steps forward... so just treat it with love and respect.
good luck
last note. PLEASE PLEASE PLEASE take care with the idea of kids manipulating you. little kids have needs. we need to make sure that we can care for their needs before thinking they are manipulating us. no tantrum, fuss, cry, or attitude change comes from the idea that the kid is thinking "if i can just do ___ mom would finally do things MY way" - kids are NOT thinking about how to manipulate their parents at this age. maybe 4 or 5 when they recognize the difference between truth and lies, yes, but not at 15 months old. only YOU know your child, and if you feel that a certain method works out, and is healthy for your relationship with your child, so be it. dont listen to any advice that makes your stomach turn or your heart break. thats the most important thing.