@jenn121,
I'm thinking the pill isn't the best form of birth control for you. If you aren't able to consistently take them then switch to another method.
As to whether you're pregnant now... if you think you conceived three weeks ago then a pregnancy test will be positive now if you are pregnant. If the light period you had was three or more weeks from the time you did the pregnancy test then you weren't pregnant then either.
When does this cycle of pills end? If it's soon then finish this cycle and see how your period is. In the meantime, if you've missed (as in not taken in a 24 hour period) two or more pills in this cycle then use another form of birth control until you begin the next cycle.
I would seriously suggest you talk to whoever prescribed you the pills about a different method of birth control. This one isn't right for you.