Ibeck,
Yes, it could be plantar fasciitis. But, it sounds like you have done most of the things that a physician would try. Since this is an inflammatory condition, NSAID's are one of the mainstays of treatment. You do not mentioned if you have taken any of the antiinflammatory medicines. Often, patients do not take enough medicine, since it has to be at a therapeutic level and then sustained for several weeks. Most patients usually take it "as needed", and therefore, do not take it such that it actually works as an antiinflammatory.
Besides the shoe inserts, which do help, the plantar fascia also needs to be stretched. This is exceptionally important upon rising in the morning. Before putting weight on your feet, stretch the soles and the achilles tendons. You may also need to do this several times throughout the day.
It is very important to wear good shoes. Now days, with all of the athletic shoes available, one should be able to find a pair that fits him/her well. If the shoes are not comfortable when you try them on, do not buy them. Athletic shoes do not need to be broken in. There are enough brands and styles out there to fit everyone. Also, the protective nature of the shoes wears out fairly quickly. Even though they may still look okay, if you are going to be in them for many hours a day, up on your feet, make sure they are still in good shape for that. You usually need to get new ones about every three or four months, depending upon your weight and activity level. The old ones can still be used to knock around the house and stuff. But, investing in good, comfortable shoes goes a long way.
There are even dress shoes out there that have athletic type insoles. If you have to wear boots for work, they too can be found with athletic insoles. Look for the ones that are most comfortable for you.
However, there are other causes of burning pain in the feet. Burning pain is often attributed to nerve damage. Diabetes is, of course, the most common cause. There are other metabolic disorders that can also cause this type of problem. The nerves supplying the feet can be compressed, causing pain and numbness.
The only way to know for sure is to see a physician. If the pain continues or gets worse, you may need to see your family doctor. Good luck.