Hello

Dear Customer
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What is your diagonsis ?
although you have mentioned many information , but its unlikely to be totally connected , such as first incidence , and was totally allergic reaction toward the medication , but later and other situations lead to an infection , you are unlikely to have IBS because its not an infection so you husband wont have the same symptoms 
- name of infection you have : its possible to have norovirus ( viral infection ) 
What do to next ?
1. reconsult an internal medicine doctor to do the needed medical examination
2. avoid fast food and stick to home well-cooked food 
3. drink plenty of fluids 
4. you may take medication to relieve pain such as ibuprofen 
5. you may also take anti-diarrhea such as loperamide
6. if its an infection , its mostly self limited and you wont be needing any further treatment 
Needed medical tests ?
1. physical examination
2. stool test
3. blood test
4. abdominal ct scan 
5, low GI scopy 
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Kind Regards

Dear customer :

we suggested viral infection according to your symptoms , but we should explain the following :
1. as my teammate suggested earlier , if previous infection or medical illness caused a severe symptoms and damage , symptoms may last that long 
2. viral infection doesnt last for one month , but recurrent exposure to the cause may cause that 
3. according to your symptoms , first your and your family symptoms suggested alergic reaction , but later symptoms appeared as an infection
4. some doctor before suggest to you to test for IBS ( ulcertive collities ) , but medically speaking , IBS isnt contagious , so your family should have the same symptoms as you in some point 

In short words :

although your infromations still not enough for us to diagnose you precisly , your medical condition for most likely to be caused by recurrent exposure to a cause , such as food , or contiminated surface or a pet , so we you should do is the following :
1. treating the symptoms , and by that we mean you have to take medication for nose itching and abdominal discomfort 
2. antibiotics for GI tract is a necessary in your case 
3. regualr visit to internal medicine doctor to do routine examnation especially if new symptoms appeared 
4. pay attention to your food , home hygine , and the same to your family 
- if you have any more information about your medical issue , please mention it so we can help you more 
best reagards 

Dear customer :

our advices remain the same according to your medical condition and new informations , and we have to mention the follwoing :
1. abdominal discomfort side effect from vitamin D intake is common and normal
2. mucus finding in stool could be a sign for many causes , starts with infection and may be GI abnormalites 
3. as we said earlier , treat your symptoms for now , and avoid fast food or not- trusted sources one 

About being afraid of antibiotics :

- usually if you are allergic to one type of antibiotics , there are other options to use and those options will do the same effect and will cover the same infection causes 
- just consult your doctor about the best antibiotic for your condition with mentioning that you have allergy to the medication you have used before 
best regards