What is the pH of your irrigation water? It could be that you have alkaline tap water, and this would raise the pH of your potted blueberry shrub. Blueberry shrubs thrive when pH is between 4 and 5.

Yes, add sulfur to lower PH, do not use tap water unless treated to lower PH with some type of acid. Do not use fertilizer with nitrates, you need urea or ammonium nitrogen sources such as in fertilizer for acid loving plants.
Also the type of blueberry may matter, if you're in the west and growing Northern highbush, you will have problems.

Are the leaves reddish in tint? If so it most likely is high PH. They should be green. A little red is OK, as long as they eventually turn a dark green.

N highbush varieties are grown in the west, even by commercial growers, but only in areas with high enough chilling hours. Southern highbush grow well in areas without adequate chilling, so Drew's statement is generally true, but I thought it worthwhile to be more specific because my sister grows N. highbush north of Eureka in CA. I'm sure N. highbush grows well in the mountain areas of the west and in the northwest in general.

Drew, when I first read your comment I didn't even realize there were southern highbush varieties. I was only aware of N. lowbush, N. highbush and rabbiteye. I knew there were evergreen varieties that weren't rabbiteye but didn't know they were called southern highbush and were bred from N. highbush varieties. From what I've read about S. highbush, you cannot grow them outdoors in areas you can't grow citrus (outdoors). Here is some information on the subject.

http://extension.oregonstate.edu/lincoln/sites/default/files/pnw656_1.pdf

Not really true some have every type in their lineage it's difficult to determine exactly what they are! I protect mine, but some like Southmoon A SHB, is rated to my zone. Southmoon is grown a lot of CA, developed in Florida. Most are rated to zone 7 and I can keep those in the garage in pots during the winter. It is warm enough in there to be a zone 7 winter. Many have not been tested, so may be hardier. The biggest problem is SHB in northern areas is the early bloomers may bloom too early. So I only grow mid and late season types. Also some are more for colder southern regions, TN, Kentucky etc. These types don't do that well in Florida or CA. They do well here. Northern types can't take much heat, so never do well where hot summers are typical.

It doesn't take years for BB to thrive, they should be very vigorous and flower and fruit like crazy. Tell us about the variety, size of the container and potting medium.