There's a sore on arm and it looks like it's a spider bite and it's really big at the head of it but does not hurt or have a warm sensational feeling?

Need a photo to dx. Most bacterial infections of the skin like abscesses are tender with touching and will feel warm. Since there is no pain, this may be an insect bite or spider bite of some sort. Try cool compresses for a few minutes several times a day. If it enlarges, a consultation with Healthtap with photos or a doctor visit is recommended.