I've been feeling really weak latley and i dont know why...plus i have this strange bump/lump on my shoulder.?

for the past couple of days i haven't been feeling myself. I didnt understand why this is happening. It all started when i found this weird lump on my shoulder that was bothering me. It felt very achy. Then when I woke the next day my legs were aching as well and around my shoulders. I just brushed it off thinking it was just growing pains. But now i feel very weak when I start walking around. Im feeling very tired latley as well. I dont feel sick ethier. I dont understand. Maybe its all in my head. My mom thinks the bump is a spider bite but i have no bite marks. Its just a bump underneath my skin. maybe its just all in my head. i dont know.