What you mentioned sounds exactly like when I was in the middle of my dilation journey. I don’t know where you live, but in my country, doctors were not even aware that I had vaginismus. So I self-diagnosed and treated myself from the information across the internet and this forum. The burning and stinging feeling you get during dilation is common in vaginismus patients. I myself experienced it and it was so painful that I lost hope, but someone in the group recommended me to use Lidocaine ointment during dilation to numb the pain and it worked for me. Slowly my muscles became less tight and the burning and stinging disappeared. This burning feeling is actually a good sign because it means that your muscles are working just like when you exercise at first, your muscles feel sore, and then slowly the soreness disappears. Keep dilating and be patient. It took me 5 months of dilation to be finally able to have intercourse, especially the last dilators took a lot of time and it was painful. It is great that you are on the 4th dilator already. Appreciate yourself for this progress. Another thing is that if a particular dilator is taking a lot of time and being painful, try to find an intermediate size dilator which is smaller than the current one you are using but bigger than the 3rd dilator. In this way, your body will get familiar with dilating easily. Don’t lose hope and keep trying! You’ll be on the other side one day!