In the case of chronic inflammation likeplantar fasciitis it is very important to offload the affected structure. I would suggest seeing a physio who is well versed in foot biomechanics who can sort you with a pair of shoe orthotics.
I'm not saying orthotics are the ultimate answer to cure all plantar fasciitis but they work brilliantly when given appropriately.
Also with the stretches make sure you don't overstretch as this is likely to hinder your progress. You can also stretch the plantar fascia by placing your heel on the floor and your toe on the wall (if you get what i mean) and then try to bring your knee to the wall... you should feel stretch under your foot. try not to overdo it.
Good luck