It could be a hip flexor strain but you are correct that it could be a hernia as the area of the pain is consistent with the area for an indirect inguinial hernia.
I had one last year and i went to my GP who ordered an ultrasound. There was no protrusion but the ultrasound picked it up straight away.
If it's a hernia then the rehab is to have keyhole surgery where they shove a wad of plastic mesh in your abs. The good news is that once it's fixed recovery is only a few weeks and the area is stronger than before and you can get back to full training.
The bad news is a week of lying on the couch in the fetal position and not being able to drive etc plus a few weeks where full extension of the torso causes you pain as the scar tissue stretches out.
Bottom line, get it checked out properly and then you'll know what needs to be done.
Good luck, hopefully it's not a hernia