it is interly posible, mental heath conditions are ficcle at the best of times. what will probaly help you most is problay intncive councling, posibly also involing things like play theripy (many of us big kids realy and play is a brilint way to express emotions). you may find a pet helps,or if you do not feel you can cope with an animal you could get a robatic pet, which are grate fun but easy to keep and don't conplain, you swich then off and they stay there till you tern them on again.
it sounds more depressive but PTSD id common where there has been trumatic events in the past. if your mood swings follow the sesons it could be posible that it is SAD which reguly gets condused for bipoler as may of the syimptoms are simmaler but SAD dose not have a manic stage. also many do not realise emaotal instability is not neccerly bipoler it could just be difficult emotions.
if you still have access to childerns sevices see if creative ways can be found to help you express yourself and suport the talking theripys which in the end will be the thing which helps you move on. keep going, and ask for a reassemt in around 6 mounths to see if the change in diagnoces was accurate.
feel free to pm me for a chat if you need a nonmedical lissening ear.