Thank you for asking your query at DoctorSpring.
The symptoms you had (and then later your girlfriend) is not very suggestive of a STD. It could be a common flu (viral infection), transmitted by close contact. However since there is a history of unprotected sex, you should get tested for STDs.
There are two options.
1. Get in touch with a STD clinic and go for a standard test which covers most of the STDs.
2. Get tested for Chlamydia and Gonorrhea in Urine (mostly already done in your case). Then after 6 weeks from last sexul encounter you can go for a HIV and Hepatitis B and C test. Also do a thorough Physical examination to see whether there is any lesions or mark. If you remain asymptomatic and tests are negative there is no reason for concern.
Do use condoms if future.
Hope this helps
Please feel free to ask followup questions.