Open wound - advice

Hi. I had a surgery, closed wound on 5th November 2018. It was a chronical sinus tract from the tailbone which had connection with a sinus tract downwards the butcrack. I had to operate about 10-13 cm, a line downward the butcrack. Most of the wound healed properly , but in the middle of the buttcrack, I have an 4 cm open wound that is 1 cm deep. It was about 1,5 cm deep after they removed the stiches (they had to open this part due to some infection). But for the last month the wound has stopped healing. It is very frustrating and the nurses have tried different wound dressing options etc. I think I eat healthy and all. Do anyone have any suggestions on what I can do or try? I shower the wound 1 time during the day and change the dressing myself. The wound is clean according to the nurses. I do sit a lot during work ,but the nurses say this shouldn't be a problem. Thx for the help.
I had this problem on my first surgery it got to the point it didn’t heal at all for weeks . Nothing they tried worked in the beginning give it time it will heal .