I relapse after every 11 days. What can I do?

just dont be harsh. relapses happen. try to figure out why it happened so next time you'll find the same situation you'll get an alert about it and you can try to prevent.
unfortunately we relapse for so many reasons, its pretty tricky. to me for example, a lack of social life is a big trigger. thats why i know i have to work on that side.
dont forget that we all have motivation to quit, but motivation often is not enough. we have to change our mind, because thats what precedes our actions. in order to do this maybe you have to change something in your lifestyle or hang out with different kind of people. you can try to start a self improvement path, dedicating yourself and your time in something challenging that keep you busy and gives you a bigger reward than pmo. so try to work on these advices. think also that 11 days is a good start, maybe before that u couldnt last more than 2 days or a week, so just consider it like a good result, just not good enough like you were wishing and start again.