Brief Answer:
Sexually transmitted disease

Detailed Answer:
Hello and welcome,

It may just be a fungal infection but only tests can confirm the diagnosis. You may upload photos of the rash for my diagnosis.
You can try using miconazole cream (antifungal) over the rash and see if it reduces the rash. What is the STD status of your new girlfriend.
In case of unprotected sexual exposure and suspected STD, the protocol is that blood and other samples are sent to the laboratory for STD testing and then a single shot of antibiotic like ceftriaxone 1g is given stat to act against disease gonorhea. It has to be done urgently as it spreads quickly. Partners may also need to be tested if your tests are positive. For you this can visit any near doctor.
Till all this done, please avoid any sexual activity until clear. Also avoid sharing clothes and towels. In future, use condoms.

Regards,
Dr Vaishalee

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