It's not easy to get into exercise but the best part is once you are in the zone, there is no going back. Even that 5 min you did, that was plenty because you did something. You got up and put on your workout clothes and your trainers. Trust me, even that can be hard sometimes. 5 mins is fine, just say to yourself, i'm gonna try again tomorrow and aim to do 7 mins. Within a week, you will find yourself doing the whole 20 mins.