I was diagnosed with cancer just a few weeks postpartum and started chemo very quickly. So, I had the hemorrhoids from the delivery + severe constipation from the chemo (very common). It got to the point, I had to seek advice from my Oncologist who said, "I don't do hemorrhoids", so I went to my OB/GYN.
In my case, because I could not nurse at that point in time, I was prescribed topical treatments to reduce the inflammation of the hemorrhoids.
I was also started on a stool softener (Senna is vegetable based) and increased both my liquids/fiber. Still, it was awful.
So, my recommendation is to eat as high of fiber foods as possible (Fiber One has some really good ones, but they're pretty high calorie carb - little known fact: you can subtract the grams of fiber from the total carbs if the fiber is 5g or greater)
Because you are nursing, I'd ask your pediatrician if there's anything that you should certainly avoid - you may need medication initially to help reduce the inflammation and to soften the stools and then use more dietary intervention once the symptoms are improved. I'd ask about fiber supplements (BeneFiber, FiberSure) to see if they're excreted in breastmilk.
Good luck. It's awful, but there is light at the end of the tunnel - no pun intended.