Red rash around penis head developing, should I be concerned?

This just started last month after I started having unprotected sex with my girlfriend. It started with a red dot and has been increasing over time. I looked up a few symptoms online and not sure it is balanitis, a yeast infection or early signs of a STD. It is not itchy nor bothers me. I've had a similar rash before due to bad hygiene but it normally went away. Can you please advise what this may be related to?

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i have the same condition. did you found what it is ?