Unable to connect to and AWS Oracle RDS instance

I'm new to working with AWS and RDS. What I'm trying to do is setup an Oracle DB instance on RDS, that part is fine but when I try to connect to it via an application I get various errors. Depending on the application I get a couple of different errors.

[Local computer trying to connect to RDS directly]

LinqPad - Connection Error: Server did not respon within the specified timeout interval. (I get this on both the Direct and OCI connection modes)

SQL Developer - IO Error: The network adapter could not establish the connection.

[EC2 instance in same VPC]

LinqPad - Connection Error: NET: Connection was refused with error ORA-12504 (I get this on both the Direct and OCI connection modes also)

I've done some research and it mostly points that the VPC isn't setup correctly, but I'm able to connect to my EC2 instance fine though.

Oddly enough, I did have one fluke incident where from my local computer it did connect, but as soon as I tried the test again I got more errors.

Any help, or new directions to look would be greatly appreciated. Will provide more information if needed also. Wasn't sure what to post settings wise. Thanks in advance.