It seems you have got Large intestinal infection.It may be due to Bacteria or Parasitic like Amoebiasis
or Giardia lamblia.
It might have acquired due to contaminated food or water.Be cautious about the food you take.Please dont eat outside food.
As large intestine is at the edges,you may be feeling a swelling near spleen ,which will be in left upper part on the edge.Splenic diseases will not cause Diarrhoea
and blood in motion.
Your diagnosis may be Dysentry
As you are doctor,Please consult your Doctor and take proper Antibiotic
which has activity against Parasitic infection
also.It should be safe as you are allergic to few of them.I don't think you are allergic to all Antibiotics.Please give history of your drug reaction to your doctor so that he can avoid it.
Wish ypu speedy recovery and good health