5 Month old Choc Lab has off/on diarrhea

Question
We have a 5 month old choc lab that had a bout of diarrhea about 2-3 weeks ago.  We had him at the vet office for his last distemper vacc 3 weeks ago and it was put off due to the diarrhea.  The vet tested his stool and it came back negative.  They gave us two types of meds and had us put him on prescription canned food for about 3 days.  The diarrhea went away after a few days on the meds and canned food.  On the fourth day we started to wean him back onto his regular food (Purina puppy chow for large breeds).  As we started to get him back on the Purina his stool started to go soft again.  Thought it may be his food, so we slowly started to change his food to a holistic brand Fromm.  We battled the soft stool for a while and finally on Friday of last week his stool went solid.  He was at the Vet on Sat. for his last distemper and 1st round of lyme vacc.  Just yesterday he had a solid stool in the morning and then when I got home from work his stool started out as solid and then went to diarrhea.  I am not sure if we changed his food too soon after weaning him off the canned RX food, but his has been on the new food Fromm for a week now, or if it is just something that needs to pass.  He has lost a lot of teeth over the weekend and is teething, not sure if there is any connection between puppy teething and diarrhea.  He is getting plenty of water (we water his dry food down), so I know that he is not dehydrated, and his temperament has not changed, still energetic and a brat.   I am holding off on calling the vet at this time, since he was there on Sat. for his last distemper and 1st lyme vacc. (his stool was solid at that time).  Has anyone else experienced this back and forth solid stool / soft stool dirreiaha?  Can you give us some advice???

Answer
I am very negative on holistic and other alternative diets.  Most of their claims are junk science based marketing hype.  They are full of outrageous lies.  There is nothing wrong with the Purina.  The dogs I have fed it to along with hundreds of others I personally know of did fine on it.  I now see thousand of dogs eating the slightly higher grade Pro Plan and doing fine.  I am in a position to label the charges against commercial dog chows as the lies they are.  I see many more health problems here from people feeding expensive chows and alternative diets than from common brands of chows.  

A frequent problem with young Labs, is foraging anything and everything much of which disturbs their digestion.  Being given treats from the table will also do it.  What I would do is switch him to a dry adult chow over a week.  Selecting a concentrated, meat based one will give smaller firmer stools, but that is not a big concern for many dog owners.  The early switch to adult chow is a well proven technique fro slowing growth promoting stronger joints.  Feed it dry.  To the extent that Labs even chew their food, dry chow exercises their teeth and jaws.  Try to keep an eye on him and keep him from eating anything except his dry dog chow.