I had a back tooth removed over two months ago the wound is still open and I'm in constant pain my dentist recommends we wait till it heals?

Oral Surgeon ASAP. The initial healing period of gums usually takes about 2-3 weeks. The major signs of infection are pain, heat, swelling, and redness. I think you need of see an oral surgeon ASAP for an x-ray and curettage of the area to stimulate some new healing. Do not delay.
Seek second opinion. Did the dentist state that you have a dry socket, and were you treated for that? Smoking is not advised, it delays healing. See your dentist or go for a second opinion if the pain is constant and the area is not healed. Many systemic medical issues can retard healing in addition.
2nd opinion . There could be several reasons for this but if you are still in that much pain I would suggest a 2nd opinion from another dentist (preferably an oral surgeon). There is a wide variation on how long healing takes especially with some medical conditions but it is best to be safe, especially if you are still uncomfortable. .