When ordering online, sizes can be deceiving. It pays to looks at the sizing information located on the website. At least that will give you a general idea of what to expect. For example if you normally wear a 2X don't assume that a 2X from every web site will actually fit someone that is a 20/22. The sizing guidelines are there to help you. The other day I saw that a 2X was made to fit a 16/18. I have also found that if you are a 2X that also wears a size 22, most times you will have better luck ordering something that is a size 22 rather than a 2X. Some sites even have their own sizing hierarchy, using a scale of 0 to 4 to represent XL-3X. It really can be confusing.
On the same topic of sizing I have found that clothes at Lane Bryant and Avenue have a tendency to run small. When in doubt order the next larger size. I know that is frustrating especially if you have just lost weight and are happy to be a size 20, you hate the idea of ordering a 22/24. However, if you want it to fit properly you may have to do so. If I am ordering for a special occasion and not sure if something is going to fit, I will order it in two different sizes to make sure that I have something to wear, vs. nothing. I just return that other one. I know that means you will incur extra shipping charges. If the occasion is important it is worth the extra money.
If you are shopping in a brick and mortar store you find size abnormalities all the time. When I go to Macy's I find that certain brands are smaller and would not actually fit you in your normal size. Lucky Brand has a tendency to run small, so does NY and Company, Alfani, Karen Scott, and Calvin Klein. On the other hand INC., and Charter Club run true to size. Those are my findings you may not follow the same pattern.
Please stay away from RoseGal. It had some cute looking clothes, but...when they arrive they are smaller than you are hoping for, and made very cheaply. I ordered a size 3X black capri. What came is something that will fit a 10 year old. I am giving it to my niece and I am not even sure that it will fit her. One of the tops I ordered came in a 2X instead of a 3X and I don't even think I will fit someone that wears a 2X. The clothes come from China, they take a long time to get here, and the quality and sizing is poor. I also ordered a couple of necklaces from them because they were unique. One broke as I was taking it off. I learned my lesson. The ironic thing is that after I placed my order I saw a posting on Facebook that warned people about the site. I wish I had seen it before I ordered from them.