Excruciating pain!

Hi. I've had an ACL reconstruction & meniscus repair 5 weeks back. I am able to perform all the exercises that the PT has suggested and the PT says the progress is good. However, I am unable to bend my knee completely still. While sitting on the edge of the bed/chair, I can bend my knee till 90 degrees; however while lying face down down I am unable to bend my knee for more than 70 to 80 degrees. My physiotherapist has been forcibly bending my knee to achieve a particular range - around 20 degrees more - after which she says that it'll be okay. I am ready to do this exercise and I am more than eager to achieve this last bit of bending my knee after the ACL reconstruction.. However the pain is excruciating and I nearly pass out every time this exercise is done - everytime I do this exercise, I am crying like anything.

Can anything be done about this? Is it taking me very long to bend my knee after the surgery? Or is this normal? Please help.