Protein is the main building block for muscles, so if you are not yet getting enough in your diet, your muscles will be weak and will struggle to do their job, causing aching. I went through a month or so of aching all the time, but as soon as I upped my protein the aching went away. It's hard in the early stages to get enough in, but persevere with cramming in as much protein as you can and hopefully things should right themselves soon, good luck!