achellis tendinitis ?

I am training for NYC marathon and I recently as of last week and now today have weird pain on my left achellis like there is pain when I walk like my shoe Is rubbing against my foot but its pain and no cut or anything.

I ran 8 miles monay with no pain. and now today walking just to the subway it hurts.

I am not the best at deep stretching or rolling out, I went to fleet feet one of the workers said it could be tendinitis and suggests resting and not running until race day. I am a little stressed and I don’t know what to do. first time running! please help <3