I'm speaking as a person who Manages employes and been through this scenario with employees and myself included.
When referring to raises, I always push for raises for employess who work hard and complete the task at hand. So it does not matter if they been there 2 months or 6 months, I will push for a raise because I still want to keep them around.
There are managers/companies who say to themselves that if they have an employee who makes X ammount of dollars and is able to complete a heavy work load, why should I pay him more, I'm actually saving money and if he leave I can always find a replacement.
Then there are other managers who say, I have this employee who makes X ammount of dollars and is able to complete this heavy work load, he should get paid more, because he may leave.
I believe you have been at your company for 3 months and you have showed that you are willing to take on extra assignments and even pursue further certifications/education, you are due for a raise.
I went through this before and what I always have done was keep my resume updated, and accessible to recruiters and sometimes you have to go to another job for the extra money.