That usually indicates decreased bile out put from liver/gallbladder. This may contribute to fatty acid deficiency (check for greasy stools). It can also be connected to mineral absorption, specially calcium and iron - these need acidic medium to be properly ionized and absorbed. Sluggish liver/gallbladder may indicate a decreased output of stomach acid, whether by restricted/wrong diet or nutritional deficiencies. Vegans may not produce and liberate a lot of stomach acid due to the smaller amounts and types of proteins they ingest. This may or may not snowball into decreased output of bile and pancreatic juices downstream, depending on metabolic type. Some stagnation and blockages may occur in the detoxification pathways. Gallbladder stones which may affect bile flow may be partially composed of precipitated calcium (unusable). This can indicate a deficiency in phosphorous among other things (proper ratio of ca:P is 10:4).

Some things you may want to try before trying iron supps is to thin out the bile to see if your stool color and wellbeing normalize. Red beet leaves are very good with this (also contained in a product called A-F betafood by standard process (non vegan). Other ways to see if you can dissolve the stones would be taking orthophospohric acid. This may also help with energy if your deficient in phosphorous.
Certainly you should take a trip down the memory lane and see if there is a connection between the symptoms you are experiencing and a consciously restricted diet, to ensure your body's demands are aligned with your conscious awareness.

Mike