You can have memory problems in a few ways. 1-Information doesn't really get in in the first place. This is an attention problem, technically, but people commonly report it as a memory problem. If you have trouble really focussing on what other people are talking about, it's attention. This involves problems in the frontal lobes of the brain. 2-The information gets in, but it doesn't get stored. This is a hippocampal/temporal lobe problem. 3-The information gets in, but you have difficulty retreiving it. You can pick things out of a list, but you can't come up with them on your own. We're back with the frontal lobes again.
If "trouble ruminating on previous years" means that you try to call up memories from the past, and nothing comes up, well, that's a memory problem. But if it means that you tend to get stuck in the past and can't get unstuck, then we're actually back to the attention issue. You can't control your attention. In the first case, you can't direct it sufficiently to what people are saying to get it in your memory. In the second case, you can't move it away from thoughts that are unhelpful.
A lot of things can be causing these problems--difficulty with attention is a symptom of most psychological problems and a number of physical problems, too. However, rumination is a characteristic of depression, which is very common, so that is a place to start. Simple fatigue or hormonal changes can do the same thing.
Talk to a doctor or psychologist. They can give you precise information and treatment options based on a more complete clinical interview and testing. However, attention problems (even those that feel like memory problems) are extremely common. So don't worry too much about them, just go to an expert so that you can shake them off.