Is my pain plantar fasciitis

Hi, I’m 19/ I am relatively light/ lean for my build and have been running 40-60 mile weeks in the trails on average for the past 6-7 months often doing 20 mile plus runs while also working roughly 40 hours a week on my feet.

I am fortunate I’ve never had any real injuries pop up but last Thursday I did a relatively easy trail run ( 60 minutes) after work with 15 minutes hard hills in the middle. While turning on the bottom of the hill after the hill climbs I noticed a slight pain in my heel that didn’t really go away- fast forward to the end of my run and for that night I was barely been able to walk and apply pressure to the heel area of that foot. The following day I woke up and completely forgot about it as felt fine but around 2/3 hours into my work day the pain was pretty unbearable when putting pressure around heel/ left side of bottom of foot.

It’s been 3 days of rest (and doing indoor biking for exercise) while also doing strength training/ foam rolling to my legs specifically my calves. It’s now Tuesday and I’m back to work and I’ve spent 8 hours on my feet ralatively fine and I’ve had not really any pain but I’m not going to run until my new trail shoes arrive as I believe overuse in my other shoes may be the reason.

I’m asking if it’s plantar fasciitis as the main symptom seems to be the heel is a lot more sore after prolonged periods of rest and for me that is the complete opposite case as on the Friday the day directly after first noticing the pain I almost fully forgot about it until 2-3 hours into work and the pain on my heel and slightly left side of foot was unbearable to stand on yet once I rested it seemed fine for around 20/30 minutes.