Constipation is almost inevitable on any VLCD - everyone finds their own way to deal with it. There is a product called 'fibre clear' you can get it on amazon and this has no calories and can be added to soups, shakes. it might help, some chemists sell it too.
Most people end up taking laxatives now and again - but remember you are not eating much so will not go as often.
Drinking lots of water helps nearly everything.
GSQ