Yes, oral to penile contact could transmit syphilis. However, in that case the first symptoms would be exactly at the site of exposure, i.e. your penis. And syphilis doesn't cause pimple-like lesions. Finally, the incubation period for syphilis is rarely as long as 3 months; it's almost always less than 4 weeks.
Since you're concerned, have a blood test for syphilis, which almost certainly will be negative. When it is, you can move on without worry.
Thx you for ur reply, u relieve my concern
Hi HowardH, recently there non itchy and non painful rash appear on my back, is it possible to be syphilis rash? I am not convenient to go for a blood test in this month. I do have a picture but i don;t know how to post it out.
Almost certainly you don't have syphilis, and syphilis rash almost never itches. We don't look at photos of rashes on this forum. Just find a way to get the blood test so you can stop worrying.