Low back pain can come from so many things associated with parasite cleansing.
1. Toxins in the muscles and nerves of the lower back. If parasites are embedded in your muscles, when they die, they release the toxins which can irritate the muscles and cause them to cramp. A muscle's first reaction to injury is to tighten up and protect the skeleton, after all, that's what they are there for.
2. Toxins from all over your body being flushed through your gallbladder and kidneys. This is usually an indication that you need to drink more fluids to help them flush out faster. Humatea is great, but if you can't afford it, any detox tea is good.
As far as the stomach cramping, you may be right about them trying to hang on for dear life. Also, as they die, the toxins released can cause your stomach and colon to cramp.
Die-off symptoms are hard, and you are going to have some that nothing will be able to help.