San&paul, you are doing a great job with your new puppy and you have already received some great advice from others. Good, natural food is the way to go as all the artificial preservatives, flavours and colours which are in processed (dry and canned) dog foods can cause bad reactions and even if they don't, are not really good for dogs.
Adding crushed egg shells or bone meal to your mixture is a good idea or, as an alternative, you could use chicken frame (or carcass) mince as the crushed bones in this mince are also a good, natural supply of calcium. I would suggest adding green, leafy vegetables (like spinach)to your mix and also parsley and watercress (if you can get it) both of which can help with allergies and itchiness.
Once your puppy has really settled with his new diet and is healthy and active, it would be even better if you stop cooking his food as raw, natural food is even better than cooked, but when/if you decide to do this, change him over gradually.
All my Cavaliers (over many years) have never had any processed food. Their main diet is raw chicken mince with crushed veg/fruit mix and raw chicken necks and they get extras added several times a week, like raw egg yolks, natural yoghurt and fish (mackerel, salmon, sardines or tuna). They are all happy, healthy and active with shiny coats and bright eyes.
Your puppy's problem of biting his back leg could be caused by pain (e.g. depending where he is biting, he could be having trouble with his patella) or it could be irritation from an allergy or bad reaction to something internal (food or medication) or something external (e.g. grass, shampoo, the material in his bedding or something he is coming into contact with). If it is an external contact problem he will probably be making it worse by biting it and you may find it will help him if you can get some anti-itchy ointment or cream to put on it. (Egoderm ointment which is available from a chemist is one which usually works well). As previously suggested, if your vet can't get to the bottom of the problem you may need a second opinion.
Good luck.
