constipation, with bad nausea, cramps, hot flashes, headache

Hi, welcome to the ehealth forum and I am glad to help you.
You seem concerned by the symptoms of nausea, hot flashes, cramps and headaches along with chronic constipation. You have also made a mention of taking treatment for hypothyroidism, fibromyalgia and IBS along with arthritis.
There is one thing very important for you to understand i.e. IBS is a complex syndrome and no set treatment works. You have to find the right combination of available therapies in consultation with your personal physician that help you to live a wholesome life.
You might be suggested changes in diet, exercise, and stress management, as well as medication. Some doctors may also recommend behavioral therapies such as relaxation, biofeedback, or hypnosis. There is also a need to take stock of any medications and co existing diseases like hypothyroidism that might also cause the symptoms mimicking IBS in consultation with your personal physician.
You need to know that if Miralax( osmotic laxative) is not working after 7 days of continued usage, they might not work at all for you. Secondly, these, if used for a long time might be habit forming and not help much in the long run.
You must consult your personal physician for definitive diagnosis and management as the same is not possible online.
Hope this helps. Take care.
Note: This post is for patient education only and no specific diagnosis is claimed thereby.