attention/cognitive problems

i am an 18 year old male and have been constantly struggling with some mental problems. Paying attention staying focused. In detail i have problem with consistent mental effort, i cannot pay attention to something for a long time without zoning out this zoning out is not voluntary is actually just happens without my consent(my brain gets tired VERY easyily).. however my attention does return and i can go on with what i was doing(so mental effort is very incosistent i guess) ... Also with distractibilty i distract very easily and often catch my self doing more than one thing at a time and never really finish anything. Another problem is with my alertness and motivation i dont feel alert often during the day ... i am also depressed at times and anxous througoutt the day .. with urges to get up and move if i dont .. then my leg twitches buh its very lil twitch so i am not really bothered but it is a concern. And also i guess because of these problems i have some what developed a social anxiety (i cant hold of a conversation for a long time because i cant put consistent mental effort into anything no matter how hard i try)

also like to mention some nasty habits i have acquired masturbation and smoking marijuana.i am trying to quit masterbation i feel the urge to do it once a week once a week. And smoke weed about once a month
these problems were there before smoking weed. i feel as if weed helps me with my problems clears my head and helps me cocentrate if i smoke very little.

plz help me