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Is the "bump' a blister? an ulcer?
Did the burning with urination start immediately after sex? or was there a delay of a couple days?
Did you have any discharge before ?
If it is just one single blister lesion it is unlikely this is herpes- which is the main "blistering" infection we see in the genital area. Herpes sores generally have a group of clustered blisters, last a few days, are painful/ uncomfortable/ itchy, then resolve
From your description I would agree that a traumatic lesion sounds likely- and any lesion could lead to pain as urine goes into the area
If you still have the blister and feel comfortable posting a pic here I can tell you what I think. If it does not go away you likely should have a doctor examine you in person as it is possible there may be other lesions you cannot see yourself.
I hope that helps.
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