If you could post a picture, that would be great.
First off, do you use aquarium salt in your water? If you do, your fish will never get ich. (However, there are some arguments that aquarium salt in every batch of water, or in tank water at all, is unnecessary. There are ways of keeping your fish healthy without salt. Your own judgement is best)
Second, you could try googling some pictures of ich and see how much that resembles what your fish has. If it is ich, it will last a week or more even with treatment. Don't get discouraged if it is ich, it's very treatable.
Keep up on your water changes for now (But watch out, some fish are easily stressed by water changes, especially fish in new environments), and be sure to pick up those flakes he spits out so it will not foul your water as quickly. If you don't have a waste remover (Looks like a turkey baster), you may want to get one (Partially to deal with ich, but in general it makes cleanup and water changes so much easier, and sometimes reduces the amount of stress your fish. But it is your decision, and water quality, as well as fish heath, arguably can be maintained without it).
Also, be careful with the gravel and the plant, if the plant is not silk. If your fish does have ich, he will try to scratch, and he may hurt himself. Gravel is notorious for that, as well as harsh plastic decorations. If your gravel looks rounded, then you should be okay.
Is your tank heated? You may want to get a heater, it aids in the healing process of ich, and maintains good general fish heath if you keep it consistent with the required temperatures for bettas.
Keep us posted, if it is ich I can offer you more advice.
I hope your fish gets better soon! :)