You could post a picture or several; it is a big help in identifying "yellow spots". My best guess is you have some sort of citrus scale; and it is the direct result of using a broad spectrum insecticide when it is not needed, thereby killing all the beneficials which help to control scale. You can google "citrus scale" and find good information on identifying and controlling it.

Weed, I just attempted to open your pics today and for some reason they won't open..I think it's my computer and not your pics. If you're seeing nibbling then something is munching on it. Is your lemon in or outside? Check for fine webbing, white cottony patches, brown/tan armored-like bumps..Shake the tree and see if anything flys around. When you check for scale, look everywhere..On the trunk, under and atop leaves and stems. When they're youngin's, they're almost impossible to spot, but as they mature, they're quite obvious. Yellow leaves are caused by over and underwatering, lack of minerals and/or nitrogen and insects. Since I can't open the pic it's hard to say..I'm trying to remember what the leaf looked like, but nothing's coming to mind. I'll try again later. When I water, I don't do so by schedule, only when soil is dry. Do you consider your soil to be well-draining? This is also important. What type of soil are you using? When you water does it drain automatcially or sit on top? You don't want it sitting.. What size pot is your tree in? Toni

Uh oh. Pictures are missing. Please try again.

yes but it needs some radical treatment. It's citrus gall-wasp. The damage they do to the branches causes all sorts of warping. The little blighters may have already fled the coop, up north here they usually hatch around Sept and start breeding straight away and re-infect the same tree and others nearby, thru to about October. There is some argument against fertilizing in late winter to avoid there being as much new material to lure them in early spring. Most info recommends pruning off all the infected material and putting it in a garbage (don't compost or leave lying around) by the end of August so maybe in Vic you're not too late. Citrus don't mind a heavy prune so go for it, and they try to re-shape it a bit, and give a good fertilize to get it sprouting again. Read up as much as you can about future prevention of the problem. I don't know that there is anything new in spraying or such, you have to be able to deter or kill the wasps, once they lay their eggs the damage is on its way. Just use a search engine with Citrus Gall Wasp and you will get lots of hits and see if you can find anything on the DPI websites.