would it be a waste of time going through formal r

It is more difficult during formal rush but if you go through informal recruitment you have a much better chance because you get to spend more time with the girls and it's much more casual. I joined my sorority as a second semester junior and it is a very solid chapter on campus. I say if it's in your heart, go for it. It will work out if it's supposed to. :-)

you should rush

As long as you have decent grades you shouldn't have too much trouble! Some chapters flat out drop all juniors, but it can't hurt to try.

There are houses that take juniors! But, you might feel a little weird. You really do a lot with your new member class when you first join, and it's hard if there is a gap between you and the others (for example, a lot of freshman live by other freshman in the dorms and can get together to do stuff, but if you're in an apartment, you can feel left out). I think you should give it a shot anyways, you can always drop if you think it isn't right for you, and it has the potential to really work out! I have some friends who joined their houses as juniors and they loved it!