What Causes Pimple Like Sores On My Inner Labia Minora?

I have 2 small whitish/sandy colored flat looking sores on my inner labia minora.I have no discharge or pain.Burns a little when urination passes over them.I noticed after the last day of my period that a small lump appeared on my lower labia minora.It wasb t visible but i could feel it and hold it between my thumb & forefinger.It was only slightly painful/itchy.I had gone to the beach and was in water,After showering is when i noticed that the lump was getting better and actually going away ,then the two white patches appeared.There was never a head,blister or pimple to sqeeze or burst and i had no discharge.I am 49 yrs old a little overweight but in good health.