There are a couple things going on here.
First off, there are many, many strands of the flu. According to the CDC:
Influenza A viruses are divided into subtypes based on two proteins on
the surface of the virus: the hemagglutinin (H) and the neuraminidase
(N). There are 18 different hemagglutinin subtypes and 11 different
neuraminidase subtypes. (H1 through H18 and N1 through N11
Influenza A viruses can be further broken down into different strains.
Current subtypes of influenza A viruses found in people are influenza
A (H1N1) and influenza A (H3N2) viruses. In the spring of 2009, a new
influenza A (H1N1) virus (CDC 2009 H1N1 Flu website) emerged to cause
illness in people. This virus was very different from the human
influenza A (H1N1) viruses circulating at that time. The new virus
caused the first influenza pandemic in more than 40 years. That virus
(often called “2009 H1N1”) has now replaced the H1N1 virus that was
previously circulating in humans.
Influenza B viruses are not divided into subtypes, but can be further
broken down into lineages and strains. Currently circulating influenza
B viruses belong to one of two lineages: B/Yamagata and B/Victoria.
So while there are only a few strains of Type A flu, there are many strains of Type B.
More importantly, the flu is very different from a cold. Typically it takes at least a week to recover from the flu, with symptoms including fever, muscle aches, and URI symptoms. It's pretty unusual for someone to recover from the flu in just 2 days-- if you got better that quickly, you probably just had a cold.