10 month old dog limping on and off over the past couple of weeks

I have a ten month old dog and recently on and off he has been limping on one of his back legs. Some days it’s fine and others it looks like he struggles even when walking around the house.
He has regular short walks as he comes to work with me and has a longer walk when we get home.
Am I walking him too much for his age or could it just be a muscle strain/pull?
I may take him to the vets if it persists but I know having x-rays etc. can be very expensive.