Are you sure it is throbbing or pulsating feeling and not a vibration - like the vibration of a cell-phone?
If it is a vibration, the sensation occurs when the muscles in that region undergo minor contractions
called fasciculations - rather like the tic of an eye.
Fasciculations in the genital area usually occurs when the nerve carrying sensation from that area is pinched or affected in any way. Infection of the nerve for example by herpes can also cause the sensation.
The nerve supply to the groin comes from various nerves all of which originate from nerve fibres from the lower spinal cord. A spinal cord herniation or degeneration of the spinal bones is often associated with vibration of the muscles of the groin.
In your case, the vibration could be due to a vitamin B deficiency caused by the long term antibiotic use.
Slow stretching exercises as well as taking multivitamin supplements containing Vitamin B1, B6 and B12 helps.
Please consult a neurologist and ask for an MRI of the spinal cord as well as to be tested for herpes.
I hope this helps.
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