first of all

i just get partied up with generals and im a major

I just dont know how people do it.

im struggling to build like 10 scorpians in the time it takes somebody to build 20 grizzlies

i just dont get it, i build a tonne of supply depot's but i just dont have enough money

I never seem to be able to rush as they just lock base then pour out counter rushing troops

+ in 3 vs 3 i get fucked because teamates suck ass (im not great either but fs my m8 thought was great idea to get gauss worthog before building a single warthog when we were rushing)

I get absolutley demolished but grizzlies most of the time, i try cobras but they dont seem to work well for me and i would most of the time get odst spammed by their teamate

If anybody could give me some tips would appreciate it

Sounds like you don't scout well enough. Scout, try to see what they're building. And harass as well; don't let them constantly build up.

Do not delay your attack. Keep the pressure on, don't sit back and let them get strong without "Getting in their face".