Relate, which provided more than 20,000 sessions of sex therapy in 2013/14, said couples often say they want to bring the spontaneity back to their love lives.
But its counsellors point out that sex is rarely truly spontaneous and busy people sometimes have to plan for intimacy.
"It's sad that so few people are sexually satisfied and put pressure on themselves to perform," said Cate Campbell, a psychosexual therapist and Relate Institute lecturer.
"Noticing what is going well, rather than dwelling on problems, is quite difficult when we're all bombarded with messages about how sex 'ought' to be.
"Sex definitely doesn't have to be disappointing - there's plenty that can turn your situation around so you can enjoy a sustained, fulfilling sex life. What constitutes a satisfying sex life can vary wildly from one person to the next, so working out what makes you tick is a great starting point.
"People may feel concerned if they 'haven't had sex in the past month but there are plenty of other ways to be sexy."
Previous research by Relate suggests a lack of intimacy in many relationships, with nearly a fifth of people saying they never or rarely felt loved in the two weeks before they were questioned.
Denise Knowles, a Relate sex therapist, said it was clear that "things aren't as good as they could be for many".
She said although people found it difficult to talk about sex with their partner, it could be the key to improving what is an important aspect of their life together.
"This can have an impact on our relationships and the way we feel about ourselves," she said.
"The first step in improving sex for most people is to start talking honestly about what you want from your sex life, and, crucially, listening to your partner's wishes as well."
- Daily Mail
