I would like to know why I don’t climax during sexual intercourse. What is holding me back? What is this blockage?

What that “block” of yours reveals is the fear of the encounter between your parts, between your masculine and feminine, as if the dread of failure were greater than the desire.

In other words, you know that You Are Everything: in the manifestation of earthly incarnation, you, like everyone else, have assumed dual forms of energy; thus, masculine and feminine energies meet and merge within you. When there is an imbalance, accompanied by fear, in the meeting of the two, an energy blockage is created.
Is that clear to you?

Yes.

Returning to the encounter with full awareness, and with the Consciousness within you through which the encounter itself manifests, allows the sexual energy to flow.

Excerpt of a Channeling from the Source session
of  31.03.2021