1 1/2 years after rhinoplasty, nose only now beginning to look crooked. How can I fix it? (Photo)

At this point, you would be a candidate for revision rhinoplasty. Keep in mind that revision procedures can be even more complex than the initial surgery, due to loss of structural support and potential scar tissue. Make sure you choose a board-certified facial plastic surgeon who has performed many revision rhinoplasties. With the right experience and qualifications, you should be able to achieve a good result from your revision procedure. 

Correcting small frontal asymmetries, as an isolated procedure, is just exquisitely difficult. But if you are considering a revision, it's helpful to look at anything that still bothers you about the nose, so everything can be addressed at the same time.You only posted this one cropped frontal view, but your nose looks long to me, with the tip hanging down. If that's on your list, then elevating the tip in a revision can help with the asymmetry, because a long nose shows more asymmetries than a shorter nose: the new position of the tip might just cover the asymmetry you notice today.The woman in the short video that I posted with this answer had the tip of her nose elevated significantly in her revision operation. In expert hands, making that change is one of the more predictable changes to accomplish in a rhinoplasty, even a revision.How *much* to elevate the tip, or even whether to do it at all? We figure that out with morphs, well before surgery. 

Revision rhinoplasty requires exceptional skill on behalf of the surgeon and great communication with the patient about realistic goals and expectations.
Common cosmetic concerns include a dorsal hump, wide nose, sunken nose, irregularities, and asymmetries. Functional concerns include difficulty breathing through the nose, which can and should be addressed at the same time as your rhinoplasty.
In a revision rhinoplasty, cartilage from your septum may have been depleted and therefore often an alternative source of cartilage is needed, such as from the ear. This is just one of the important differences between primary and revision rhinoplasty that need to be discussed in detail before you decide to proceed with surgery. 
In your situation, cartilage has memory and can shift over time. There is no non-surgical way to correct this. A revision procedure would be required to re-straighten your nose.
Make sure to seek out the care of a board certified surgeon with extensive experience in revision rhinoplasty. Find someone you connect with, who will listen to your concerns and provide you with a framework for what is possible.  
Gary Linkov, MD
Rhinoplasty Specialist
Manhattan