You may start with other paid ads but I doubt that you can earn much from it in just 3 month, unless you are very good in getting traffics to your blog. One of the reasons of having you to post as much as possible for the first 3 month is to prepare your blog to be accepted into pay to blog sites. PayPerPost, Smorty and BlogsVertise are my top picks. There are many pay to blog sites that you can find but these are the best that I found.
There are news regarding those blogs that involve with PayPerPost are being penalized. Blogs that are having sponsor text or banners of PayPerPost are being hit by page rank down by Google. Well, if your blog is just 3 month old then you don’t have to worry about it too much. You’ll be the last to be hit by this effect. Besides your blog is still too young to be notice. By the time that your blog received a lot of traffic, solutions to this matter might be available then.
The most important thing right now is to get your blog ready with lots of good content and work your way to getting more traffic. For a 3-month-old blog, pay to blog is considered the best earning opportunities.
P/S: Smorty is no longer available.