Brief Answer:
Might be related

Detailed Answer:
Hi,thank you for posting your query on health care magic.

I can understand your concern.

You suffered from back to back cold and then diarhoea.Both can be related to each other in following ways:
1.)The symptoms we get during a viral illness are often the body's attempt to get rid of the virus and to minimize damage. Sneezing ejects the virus from the nose, cough from the lungs and throat, vomiting from the stomach, and diarrhea from the intestines.
2.)You might be suffering from Viral Gastro-enteritis(inflammation of lining of stomach and intestine) preceded by a viral infection in nose.

You have taken Decongestant.It might be containing Pseudoephedrine.In few cases,pseudoephedrine might cause diarrhoea.

Looking at your symptoms,it might be due to viral infection.
Signs of bacterial infection in Gastro-intestinal tract (i.e, high fever, bloody diarrhea, severe abdominal pain, >6 stools/24 h) are absent.
Also signs of bacterial infection in sino-nasal cavity are absent like:
Onset with persistent symptoms or signs lasting for ≥ 10 days without any evidence of clinical improvement; or
Onset with severe symptoms or signs of high fever (≥ 39°C or 102°F) and purulent nasal discharge or facial pain lasting for at least 3-4 consecutive days.
So,at present you need not take Antibiotics.

In the treatment for Diarrheoa - the main objective is to maintain adequate rehydration and electrolyte supplementation. This can be achieved with an oral rehydration solution (ORS)

Oral rehydration is achieved by administering clear liquids and sodium-containing and glucose-containing solutions.

A simple ORS solution may be composed of 1 level teaspoon of salt and 4 heaping teaspoons of sugar added in to 1 liter of boiled/packaged mineral water.

Medicines like Antisecretory agents, such as bismuth subsalicylate (Pepto-Bismol), and Loperamide (Imodium) ( It increases the intestinal absorption of electrolytes and water and decreases intestinal motility and secretion) may be useful.

During episodes of acute diarrhea, patients often develop an acquired disaccharidase deficiency due to washout of the brush-border enzymes. For this reason, avoiding milk, dairy products, and other lactose-containing foods is advisable. Strict personal hygiene should be practiced during the illness.

For cold and sinus symptoms: You may get relief by taking Nasal Decongestant drops(like Xylometazoline) if you are not suffering from high blood pressure, Antihistaminic (like Cetirizine),Mucolytic (like Ambroxol),Antipyretic like Paracetamol if you are suffering from fever and Saline nasal drops.

Drink lots of fluids,do steam inhalation,Avoid dust and other pollutants.

Hope this answers your query.Get well soon.

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