I have a female boxer that's itchy all the time.
She for sure doesn't have flees. She also itches her back and sides, and it can come on very suddenly.
This use to only happen in the spring and fall however this year she has no relief.
She doesn't scoot her butt and there's no irritation around the anus. I feel so bad for her and don't have any ideas.

It could be an infection next time she does it try and have a look or she might have sat down somewhere and a chip of wood or something got stuck might have to take her to the vet if don't get better.

You have just described a typical case of allergies. First it only happens for one season. Then it's two seasons, and eventually it's an all year deal. Boxers are not resistant to developing 'atopy', which is the 'correct' term for hay fever like allergies in animals. Unlike people, dog allergies affect only the skin, not eyes and respiratory signs.

The all year allergies are from something that is present year round, and are usually only indoors. Molds and house dust mites are the most common. The mites are universally present, invisible creatures, that live everywhere there are people living. It isn't the mites, it's their dead skin and droppings that are found in all house dust to which dogs, and people, develop an allergy. The molds are very specific allergens, meaning one type of mold, like the black mold around a refrigerator seal, may be the only mold out of all found in the house to cause an allergy.

Treatments for allergies would be unnecessary if you could either move to a place there were none of the allergens, or completely remove them from the dog's environment. CONSEQUENTLY, we have to resort to some other measures. Medicines or vaccines to build up the dog's immune system against the allergens (just like to measles and other diseases for people). Medicines such as cortisones are effective but discouraged for long term use as they are damaging to the kidneys and liver. Anti-histamines are safer but not as effective in more severely allergic animals. Vaccines offer hope for permanent relief from the itching, but are expensive, may take a year to fully eliminate the itching, and usually need to be added to as allergies continue to become more widespread as the dog grows older. (new allergens need to be added to the vaccine regimen).

And then, there are food allergies that can cause itching as well. But they are a bit different, and less common.

Your vet is the place to go for advice on handling allergies and testing, should you want to go that route. There are two types of testing: skin and blood tests. In the hands of an experienced vet, skin testing can be equally effective as blood testing, but is not, essentially, more accurate. Testing can be only as 'correct' as the number of allergens used in the process. An accurate diagnosis is essential to developing a fully effective vaccine.