I had a lymp as big as small marble come up on my forearm, very tender to touch, no redness, went down in about two hours. you can still feel a small ?

Not a lymph node: There aren't any lymph nodes in forearm. Possibilities include reaction to an insect bite. As long as it's improving would not be concerned.

? contusion: Most often a transient lump is the result of trauma/an injury or contusion, even if you can't recall something like that happening. The injured tissues swell, or there is a broken blood or lymph vessel that causes a lump. It is quite reassuring that it essentially disappeared so quickly. It is not surprising that a small focus can still be felt. You can watch this.