Take a pregnancy test. Either a home test or at the health department. In Georgia you can get a preg test at the health department. If it comes out negative you just pay something like $28 if it's positive and you plan to apply for medicaid you don't have to pay. A home test would be cheaper and just as effective if you get a good brand. I've know of several women getting preg after having tubes tied.
I've had my tubes burnt for a few months now and I barely get a period, ever. My doctor told me that hormonal changes can make you feel pregnant, but that it is highly unlikely. If you truly believe that you may be pregnant, take a test!
I have a very good friend who had her tubes tied, and then, when she was 39, discovered that she was pregnant with her son. She calls him her miracle baby, although after he was born she had them burned just in case.
Though it would be highly unlikely that you are pregnant, there is always a slight possibility since you tubes were tied and not burnt. Sometimes (in rare instances) they do grow back. Since you don't have any insurance, you could take a home test.
There is always the possibility that your cycles are just changing too, but to be sure, I would take a test. Good luck!