Thank you for this information.
Grass eating can be normal for some but may also indicate increased stomach acid and/or nausea, especially if they are suddenly much more interested in grass eating than they used to be.
His symptoms are quite vague and non-specific but it does sound as though he is remaining happy and well throughout which is the main thing!
Given how long he has had symptoms for, it would be prudent to ensure his weight is staying the same (you can usually check this at your vet free of charge or use scales at home if you have big enough ones and know his previous weight) and he is continuing to stay well hydrated (his gums should be nice and wet when you touch them rather than sticky/dry).
Probiotics will certainly not do any harm and may help. The best ones contain ingredients to stop frequent/runny poo and also contain good gut bacteria. I recommend Protexin Prokolin or VetPro Digestive Function or Canigest. Most will only need a 2-3 day course and can be purchased online, from pet shops and from vets.
Probably the best food to trial at this time would be a bland, sensitivity diet such as Hill's I/D or Royal Canin Gastrointestinal. Most dogs prefer the wet versions and warming them slightly before offering them can increase palatability. To ensure he is consuming enough of his food, refer to the chart on the back of the tin which will tell you how much a dog of his size needs. Avoid indulging him with chicken/tit bits to ensure he does eat his balanced dog food. If absolutely necessary, a small amount of chicken could be mixed in well to encourage eating if her otherwise refuses.
If things to not improve dramatically quickly, we really would need to look into this further. It may be that he has a sore tooth, foreign body in the mouth or grumbling pancreatitis; all of which would decrease appetite. Of course, there are many other potential causes. If signs persist, the best course of action would be a general vet check from nose to tail and a basic blood test. If nothing is detected, a trial of anti-nausea/ant-acid medicine may be suggested, especially as he has been munching on a lot of grass recently.
Given that he has been scooting, we would also want to check his anal glands. Anal gland impactions and infections can cause a lot of discomfort and may well lead to reduced appetite.
As a final note, with regards ***** ***** he has had, I would just want to double check that this is a good quality product (such as Panacur or Drontal Plus) and that it was given within the last 3 months?