Hi,Rinki,thanks for query.There could be various reasons for this like anxiety
,tension,some social stress
,pressure due to domestic issues etc.Please talk to your partner about this and try to discover time convenient to both of you.In stead to doing sex at night,try early morning sex as both of you are fresh and stress free.Spend more time in foreplay,try to explore your erotic zones and take more interest in the act.Remote disliking and phobia
from mind.You should try new positions,new time,new place etc.
wishing you good health.