Hi Justo,
37% of your net wages is a meaningless figure.
If your net wages are 10,000 per month then you should be well able to manage with 37% of this for food, clothes, etc.
If your wages are more like 2,000 pm then it's a whole different story.
Do up a list of all expenditure on an average month - food, clothes, electricity, petrol, everything. The bank will not expect or require full mortgage payments at the expense of you being able to feed your family. I have found them to be very sympathetic to a family which is struggling.
Of course going interest only for a few months or so will mean paying more interest in the long run but once your car loan is paid off you can revert to capital plus interest and won't be paying much more each month.
My advice would be to get all your figures together and approach them immediately - they like people to be proactive and sort out problems before they become arrears.
Sybil