She had been taking Depo shots every month the entire pregnancy (remember, she didn't know she was pregnant) and she had a very sweet, healthy, but TINY little baby
That being said, you need to get a preg. test (though late in pregnancy
some women's HCG levels dip). The only way to know for 100% sure you are pregnant is to see a doctor and to get an ultrasound. You could also have fibroids and be mistaking it for pregnancy.
So definitely get a test, then let us know what is going on!