Hello, as a licensed veterinarian I am happy to assist you!
Dry, itchy skin on the back at the base of the tail is highly suggestive of fleas. If Bog Boy is not on a monthly preventative flea medication, I therefore recommend he be started on one and kept on it for a minimum of 6 months. It may also be necessary to treat the house (choose a pet safe product), as fleas are great at living in carpets, nooks, and crannies and eggs can hatch inside throughout the year leading to re-infestation if they are not taken care of. These products are available over the counter online or at pet stores. Some great products include Frontline and Advantix (be sure to choose the cat product, not the dog one). Additionally, depending on where you are located, heartworm
prevention may be ideal for Big Boy, in which case you may want to talk to your vet about a combination flea/heartworm preventative (available by prescription only)- if you are in the US, then your pet should ideally be on heartworm preventative.
To help with the dryness of his skin, you can also give him a fatty acid supplement. These supplements help with dry skin and coat, and with overall health and healing of the skin. **Please note that this will NOT treat fleas, so this should be given in addition to the flea preventative.** The easiest way to properly dose a cat is to buy a pet specific product and dose according to the package. Here is one such product (but there are many other options): http://www.amazon.com/EFA-Z-Plus-Fatty-Acid-Supplement/dp/B001ENIJW8/ref=sr_1_2?ie=UTF8&qid=1435846960&sr=8-2&keywords=cat+fatty+acids
Thank you for your question! Please feel free to respond with additional questions or concerns. Once you are satisfied with my answer, please remember to rate my answer so I receive credit for my time (I receive no other compensation).
All the best to you and Big Boy!