I sympathise greatly op as I am a sufferer too. Mine was definitely stress related (suffered with severe anxiety on and off and some depression) I had to go into A and E once because I was so blocked and it was very painful and I had to have an emergency enema. Once I am unblocked it appears that with rest, relaxation (maybe mindfulness) combined with the right diet including lots of water, vegetables and maybe a supplement of Fibrogel, while the bowel "recovers" this has helped. I really don't suffer very much anymore. I have found that dealing with anxiety issues, water, exercises (walking is great, depending on your fitness levels running is better) but really it was a combination of things for me, but I really feel personally that it was linked to depression as well as diet and exercise. I think it is possible to improve it, but it takes time and maybe you need to find out what works best for you.
Maybe a food diary to work out for yourself which are your trigger foods? I am now following a GL diet, I don't eat sugars, wheat and lots of veg. White potatoes, white rice and white pasta, I have found, personally speaking are big "trigger foods".
I think also, just to add, while you are more chronically constipated, a gentle solution such as a glycerol suppository is helpful to some people. Also you can get small "micro-enemas" from pharmacists in the UK, I believe, but as always it's best to find a medical professional to talk to about these interventions and if they are healthy for you in your particular case.
Good luck and I hope you find a solution that works for you.