When is viral infection contagious?

Viral Infection

I am not sure whether I am having a cold or flu. It started 2 weeks ago. I thought it is probably a simple cold or flu and I bought some Panadol Cold Reflief tablets to take. I thought it is nothing serious and does not need to see Doctor, and so I just bought over the counter medicine from the Pharmacy of a Hospital.

I am not really coughing but seems to have very thick phlegm that I have difficulty coughing out. When I managed to do see it is pale green color. I just took some cough mixture initially.Sometimes my voice is very hoarse.

When the phlegm didn't go off and continue to be there daily even though I have cough them out, I begin to wonder whether I should see a Doctor after all. So yesterday I went to a Clinic near my home and saw the Doctor. After seeing the phlegm, the Doctor said I have a viral infection and prescribed me an antibiotic and cough mixture. As I am asthmatic, he also gave me some steroid to prevent relapses or complications of asthma. 

I wonder whether I can go out with my current condition. I  wonder when is the viral infection contagious? Will I pass the germs or virus to others if I go out. So I did a search on the internet and found the following website and information:

1. Am I Contagious? When to stay home sick
Both the common cold and the flu are caused by viruses. Viruses can easily spread from person to person—either through the respiratory system or through direct physical contact. If you have a cold or the flu, you are contagious.

There is a chart on this website that lists some of the symptoms of flu, cold and allergies. Some of these symptoms are quite similar. Basically, when one has a cold or flu, he/she is contagious and it is important to stay at home so that he/she does not infect others.
While cold and flu last three to 14 days, seasonal allergies often last for weeks. Grass pollen season, for instance, lasts six weeks. For allergies it is okay to go out as it is not contagious

Now I understand a little bit more. For more information read here