Thank you for the information,
There can be a few possibilities.
Shaving can initiate razor bump.
This is due to irritation from hair growing back into skin.
Though it is not clear from picture, but it seems more in the hairy part of the penis.
So it can be razor bumps.
An allergy is also possible.
This can be due to bacterial infection like folliculitis but you are not having any pain.
As there is no clear fluid or pain, it does not sound like herpes too.
Wart can form there.
As your recent tests for std were clear & your partner did not have any such history it may not be std.
Still, you need to get those checked by doctor.
If he thinks necessary, he can advise tests again.
Antihistamine like zyrtec or benadryl will help if it is due to allergy.
I hope this information helps.
I will be happy to assist, if you need any clarification.
Please feel free for any follow up query.