If I have only been married for 3 months and want out, would I get a divorce or an annulment?

There are several grounds for annulment, you will need one of the grounds or more to get a marriage annulled. Based on the limited facts provided, you do not meet the length of time grounds of 72 hours. You might meet other grounds based on the facts of your case but you can always get a divorce anytime.

Is the 6 month old from the same person that you are married to? You should be able to get free legal help on base from JAG for divorce and/or annulment.