Hi, sorry for the late reply. I don't experience any pain with it, and I am also not sexually active. I am female, but do not smoke and am not obese nor do I have any other vascular issues that I am aware of. I have noticed this happen in the past and it appears to happen one day and then not again for a while. I haven't experienced it since the day I posted this.
I would like to add that I've sneezed twice today and felt a similar pulsing feeling there.. It only happened after the sneeze and didn't happen again until the second sneeze.
I'm going to assume by your name that you're female (?). You mentioned the sensation gets worse with sneezing; do you get a sharp pain before the "pulsating" begins or does it just continue to throb at the same level of pain? If you get a sharp pain followed by the pounding afterwards, it could be an umbilical hernia (a tear in your stomach muscles that hurts worse with strain on those muscles).
If not then are you sexually active? You may have some type of STD or PID. You can buy test kits OTC to test for this from the privacy of your home if you refuse to seek professional medical help.
Given your age, the probability of an abdominal aneurysm is very low. If you smoke, are obese or have any previous vascular history, the chance is increased, but if you are otherwise a healthy person I wouldn't worry too much about this.
Obviously if you notice the pain getting worse you should immediately go to an ER where they can do the testing you need for a real diagnosis rather than the guesswork you will get online from those of us with only a portion of your history.
Hope this helps a little! Feel better.