(hypothetically), if a condom was already used once, and the guy had a small penis, is it still reusable?

(hypothetically) NO.

(hypothetically)What would be the consequences?(hypothetically) The condom doesn't hold that strength any more, it could break or stretch too much.

(hypothetically)Would a 16 year old girl be less fertile after or before her period?(hypothetically) Typically, neither. You tend to be fertile right in between periods, which is when you're ovulating.

(hypothetically) And if a condom breaks and you dig the semen out, can you still get pregnant? Dig the semen out? *cough* No, you might not have gotten it all out.

(hypothetically)Does birth control protect against HIV?(hypothetically) NO, it definitely does not.