If you both had no previous partners, even for oral sex, you can't have an STD.
STDs need mouth-to-genital, genital-to-genital, or genital-to-anal contact to transmit. Just like a cold or strep throat, you need to be exposed to the germ to get it, which means that one of you would have had to have one of those kinds of contact before to have an STD. They don't just develop out of nowhere.
Does manual sex mean you used your hands? That's called mutual masturbation (masturbating each other) and is never a risk for STDs.
I don't know your gender, but since you're on this path, actual intercourse (if you haven't had it already) may not be too far away. Consider talking to your gf about birth control now. At 14, she may need a parent's permission (that depends on where you live - don't tell me where you live, but you can google "birth control parent permission" and where you live to find out the laws in your area.
Exploring your sexuality isn't a bad thing. It just comes with responsibilities that sometimes, at 14, you may not be ready for. It's awesome that you are asking questions, and want to know about STDs. That's fantastic. :)
I'm happy to answer your questions, but Planned Parenthood has a Teen Center with a ton of questions already answered - https://www.plannedparenthood.org/learn/teens If you have any questions, let me know.