16 week old kitten with bloody diarrhea

I have had James for a few weeks now and he has had constant diarrhea with a little blood.. the blood is red and not mixed in to his stool.. It comes out closer to the end of the bowl movement..

He was dewormed with Profender before I got him at around 9 weeks old and I took him to the vet when I noticed it the vet gave me Strongid T(The vet originally gave me Dolpac but I retuned it as it was off label and that made me nervous)  he has been given this once and his second dose of it is on Friday.  

His poo is also ridiculously bad smelling, worse than any other cat that I’ve been around

He is on GO grain free cat food. The canned I feed him is all different brands but most are grain free and he gets mostly canned, the dry is just down when I’m at work

I’ve also been giving him probiotics twice a day, human grade 5 billion cfu daily

Should I be taking him back to the vet ASAP? Or should I wait until I give him the second dose of meds?

I should add the diarrhea is the only thing wrong with him, he is a normal kitten otherwise nothing but trouble lol very active and is gaining weight and eating very well.

The most common cause of diarrhea in kittens is parasites. Some parasites are not taken care of by the regular dewormers. Did the vet test for tritrichomonas foetus?  That requires a special PCR test, not just the normal fecal float done in the office.  It also tests for giardia and other hard to get rid of parasites like coccidia.

Here are a couple of helpful links for you:

Tritrich info from Texas A&M Vet school:  http://vetmed.tamu.edu/gilab/service/assays/tritrichomonas

Info on coccidia http://www.petmd.com/cat/conditions/infectious-parasitic/c_ct_coccidiosis#.Uh4mVH_KE1I

Just an update on this, James is no longer having diarrhea and the vet gave him clear bill of health

We think that the diarrhea was initially caused by worms, but even after deworming was prolonged by him sneaking into the ferret cage and eating Origin dry cat food which was to rich for his system. I noticed him sneaking in and eating her kibble and when I put a stop to that, his poo was normal the day after.