Hi,
It is absolutely normal that hair does not grow at an even length. If you think of the shape of your hairline on your neck it may be the shape of a ‘W’. To have even growing hair it should be cut regularly to even it out and also to cut off any unwanted split ends or dryness.
You should have your hair cut every few months. It doesn’t have to be much if you are growing it, but it will keep it looking a nice and even shape.
It is normal, especially with very long, wavy and thick hair that it will take longer to rinse shampoos and conditioners out. Maybe apply less on the back of your head which should make rinsing it out easier.
The normal hair growth is around 1 centimetre, or ½ inch a month. If you have not had a haircut for three years your hair should have grown by about 36 centimetres or 14 inches at least by now.
Do you use elastic bands to tie your hair up at all? This could also be the cause of your hair breaking where the elastic holds the hair together. It may be that the shorter hair at the back could have broken off due to this.
From what you wrote your hair seems really long and beautiful. It is very important that you condition your hair regularly. Pollution in the air can dry out hair and cause damage so it is advisable to spend extra time by applying a deep penetrating treatment, especially to protect the ends from drying out.
I hope this help!