Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for Syd.
It sounds as if Syd may have an issue with his anal glands especially if the area involved is under his tail. If you are not familiar with these glands, the following link discusses them in detail. http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=625
Some dogs are extremely bothered when these glands fill up which causes pressure on their bodies and will continue to do so until they are emptied. Their excessive interest in the area is their attempt to empty these glands but they frequently are unsuccessful.
Although a groomer can provide this service for you, they usually attempt to empty the glands externally. The better method is done rectally which is how a vet tech or your vet would empty them.
If you can't have him seen today so that a rectal can be done to evaluate his glands (or even if you can), I'd clean the area with warm water or unscented baby wipes.
I'd also apply a small amount of otc cortisone ointment which may reduce the inflammation. It won't be harmful if he licks it off but it won't be absorbed so distract him for 5-10 minutes.
If Syd isn't currently taking any steroids or nsaid medication and isn't vomiting, then Aspirin can be given which may help to reduce the inflammation and provide anti-pain properties. The dose would be 10 mgs per pound of body weight twice a day, with food to avoid stomach upset. For example, the dose for a 70'ish pound lab would be 2 of the full strength (325 mg) tablets twice a day.
If he's biting on top of his tail, then he may have picked up a few fleas and has Flea Bite Dermatitis. If this is the case, let me know since this particular issue will require a different approach.
I hope this helps. Deb