What should I do if I have a stomach ache, loss of appetite and constipation despite trying a laxative, while trying to become vegetarian?

Good morning Mrs. I believe that your situation deserves the attention of a doctor. As senna can cause cramps and sometimes even stomach aches, I would recommend that you discontinue its use and instead make sure you increase your fiber and fluid intake. Take steps to see a doctor and in the meantime, go see a pharmacist who can recommend a more appropriate laxative if the constipation persists despite the above mentioned tips.