I had safe sex three weeks ago, starting to feel a slight tingling at tip of penis, no other symptoms. should i be concerned for sti?

Not an STD symptom: STDs don't do this, and too much time has passed. And since the sexual exposure apparently was safe (by which you presumably mean there was no penetration, or a condom was used), the chance of any STD was low to zero. Symptoms like this often are psychological, especially if there is anxiety or regret about the sexual exposure.