Sounds quite possible - depression often causes those symptoms and most doctors will want to exclude depression as a cause before jumping to ADHD as it is a much more common diagnosis in older folks (judging by your typing you're out of primary school ). Also for ADHD to be "official" some symptoms of it have to have been present since childhood.

I sort of went the other way. Treated for depression (which was definitely depression) and hoped that sorting that out would give me an attention span. Wrong! Somehow I made it through high school and pharmacy school without listening to lectures or doing any study at home.... but this year I started med school and it requires a bit more of me. When I discussed the possibility of ADHD with my psychiatrist he agreed and said he'd had it in the back of his mind for a while.

Then at my first visit to him after starting Ritalin he said it was the first time he'd ever seen me sitting still!

However back to the original topic (oh golly gosh there's me getting distracted!!) - depression causing my lack of concentration was much more likely than ADHD. However in the end it seemed to be both! One of the favourite sayings at med school is "When you hear hoof beats, think of horses not zebras"....