Detailed history and clinical examination is needed.
Blood in stool with pain abdomen has many causes.
You also complains of recurrent burps, Internal hemorrhoids may cause blood in stool which you don't feel exteriorly but there may be other causes like IBD, Ulcers. Sigmoidoscopy is usually done to visualise inside mucosa.
Next Steps
Should see a Gastroenterologist and get sigmoidoscopy done.
Health Tips
Blood in stool has many causes , in young age group majority are benign but serious causes are also seen in few cases.