My 16 week old baby just will not be put down. Yes I have a sling but there's a limit to the amount of stuff I can do with him in it and it kills my back (it's properly fitted, I went to a sling library and have two different ones). He's a heavy baby. Every time i put him down he kicks off. I haven't got any family who can help. He's my second baby but my first wasn't like this. I'm losing the plot.