I had this when I was in my early 20s and it flares every now and then, but I was working 2 jobs, one in retail and one in a restaurant and I drove about 3 hours a day which can aggravate it also. I think I spent about 18 hours a day using my feet.
I went to the doctor, then I went to the orthopedist and they prescribed custom made orthotics. These were $300 in 1999, but they helped so much! I mean to wear them hurt, I couldn't use them for more than a couple of hours at first because they stretched out the plantar tendon, but, after a week or two, I wore them always. I haven't had the PF come back for more than a day or so since then. I do wear good shoes, and I do have ankle problems from tearing the tendons twice, but the PF is totally under control. The fancy shoes do help certainly, but if it were me, and I had to do it all over again, I would buy the specialized orthotic inserts from the podiatrist or orthopedist, and wear those. My aunt developed PF right before I did, and now, almost 20 years later, she still has problems because she went the Birkenstock route instead of the orthotics. I have heard good things from the Good Feet store, but my daughter's orthopedist said that the custom made ones are so much better because they really fit each person. (She has flat feet and has been wearing her orthotics since she was 4) and they make a huge difference for her too, including her feet, legs, ankles, and knees. They are all connected.
Before you can get to the doctor, using really tight ace bandage, or the kind that sticks to itself, can help support the arch. I could NEVER handle the cold stuff since it causes cramping, but the tennis ball was helpful. I hope you get relief soon! Also, sitting at a desk can bend the leg at the hip and this can tighten the muscles from the low back, butt area and this can also affect the heal and cause pain. I deal with this type of pain daily, and the only thing that helps that is massage on the hip and butt. I wonder if you are getting both kinds at the same time to make it worse.