A series of short nipple hints, suggestions. - Channel, Smile

If you are trying to advance times in your (self-) clamping, you could try shorter times, with more intense clamps - or whatever you are using. Remember that over 15 minutes is not recommended, due to possible circulation problems.

Personally, I use mini hair-grips, and 3 minutes is challenging.

So, use a timer (there are many online) and pick an achievable time (such as 4 minutes).

When you apply the clamps, try to remain calm, and do a gentle smile. This relaxes the face.

Writhing around does not help, swearing under your breath does not help - sit or lie calmly.

Then, you might try to channel the intensity to other parts of the body, such as the 3rd eye area, or the top of the head, or the anus, or - for men - the penis.

To give your mind more work to do, try to refine the area. For example, try to identify the tip of the penis, then the very tiny point at the tip of the tip. Imagine the intensity going there.