I have plantar fasciitis which has led to heel spurs, and what you are describing sounds similar to some of the symptoms I experience. In my case, it is chronic and bilateral, resulting from what appears to be early stage rheumatoid arthritis (bloodwork shows some elevated levels, but more specific testing is inconclusive), and is aggravated by my weight. I was also found to have low Vitamin D.
You can see a podiatrist or an orthopedist (sports medicine specialist might be best, since it seems related to your power walking), and they may want to do X-rays. There are other things that could cause similar symptoms, though; so it is best to describe your symptoms in as much detail as possible. One classic symptom of PF is that it tends to hurt worst in the morning, because that fascia stiffens up overnight.
If it is PF, resting the foot to allow it to heal, and performing specific stretches are the typical treatment. Getting better cushioning in your footwear is the best way to prevent it from re-occurring… “good shoes” is a completely relative term that is not determined by brand or price tag. There are devices to wear at night to keep the PF stretched that are also helpful.
In my research and experience, it seems that there is great variability in the causes and the effectiveness of different treatments, so there is a bit of trial-and-error in finding what will work best for your body. I hope you feel better soon!