What is the G-Spot and how can one stimulate it?

The G-spot or the Grafenberg spot is an area of increased sensitivity with maximum potential for arousal. It is located on the anterior vaginal wall about two inches from the introitus. After sliding the fingers in that position and with forward, backward or side-to-side movement, the female will be able to pin point the spot where she appreciates increased sensitivity. With increased stimulation, the G-spot swells like a nodule, and becomes firm. Simultaneously clitoral stimulation can enhance sexual pleasure.

What is the most common female sexual problem?

As per my observation, painful sexual intercourse leading to vaginismus is the most common sexual problem.

What could be the cause of excessive vaginal lubrication during sexual intercourse?

Physiologically, lubrication occurs in the vaginal walls during sexual arousal. This could increase in certain conditions of heightened sexual excitement and vaginal infection/allergy. The best thing is to find the cause and treat it. At times, a small dose of an anti-histaminic may prove useful.