Social media data have been used in research for many years to understand users' mental health. In this paper, using user-generated content we aim to achieve two goals: the first is detecting moments of mood change over time using timelines of users from Reddit. The second is predicting the degree of suicide risk as a user-level classification task. We used different approaches to address longitudinal modelling as well as the problem of a severely imbalanced dataset. For the first task, using BERT with undersampling techniques performed the best among models tested, including LSTM and random forests models. For the second task, extracting features related to suicide from posts' text contributed to the overall performance improvement. Specifically, a feature representing of a number of suicide-related words in a post improved accuracy by 17%.