Sick German WH Pointer

I have a GWHP that is about 1 1/2 years. She gets extremely sick every about three months, she suddenly gets listless and dehydrated looking ( loses her bushy look ) with a temp over 105 and a real hang-dog appearance also she is sensitive to the touch in some areas. The last two times she has developed a large pus sac somewhere on her body. She has been xrayed, blood drawn and to three different vets, all stumped. The first test about a year ago showed only a very high phosphorus level since then all levels are normal. One theory is that she has ingested something that it works its way to the surface causing the pus sacs. Another is that she is a dog that is constantly rolling on the ground and may have cactus thorns or some seeds enter her in that manner but we have never found anyting when draining the sacs.This condition usually occurs after a fair amount of exercise. I have been around dogs and livestock all my life and have never seen anything like this. Thanks for any ideas. Ed

When she gets the lumps, is there any sign, if you can examine the skin, of an insect bite, maybe a spider bet that is getting infected? I've had a mosquito bite do a similar things a couple times in my life, as I have very sensitive skin and it doesn't take much. And when it gets infected, of course, one's whole immune system kicks in ...

In what part of the country do you live? Different critters in different places ...