When I was new to Trimix, I found I had that stinging when I injected it in the wrong area. In my case, it was too deep. I found for me, I have to insert the needle at the 10 or 2 o'clock position and insert the length of the needle but just until the syringe reaches the skin (no depression of the skin). After having done it so many times now, I can feel the slight resistance when the needle penetrates the erectile tissue. After the injection, make sure you massage your penis and the base area to distribute the medication and stand while you are doing this and for the next 5-10 min. Don't give up.