Hi,Johan,thanks for query.Your guess is right.You must be having some
stress.It is always told that sex lies between ears not legs.Please try
relaxation techniques,talk to your partner and try to solve it.At times some monotonus act can lead to some boredom and loss of interest in partner,so always try to do something new.Try to sex in morning instead of night,in morning the levels of male hormones are high so that you will feel more comfortable.Also look for your weight,blood pressure,
lipid profile also.
wishing you good health.