TMI : HELP! What is this? (hoping not sti...)

Hi all!!! So I noticed this bump a bit ago, and assumed it was an ingrown hair.... however it did not go away. So finally I went in with my phone and took a picture since I cannot just simply look down there. 
Be honest -- should I be worried? I am thinking it is a wart or something... 
My partner and I have been together for almost 7 years, and have never had issues of cheating (I'm 100% certain). So I don't think it should be an STI, but it concerns me
Another possibility is I had planters warts on the heel of my foot - is there a possibility  it is just a planters wart? 
* note that this is the only one and has been the only one since about January -- it hasn't spread
Sorry about the TMI