I would take it to a local nursery and ask the horticultural people there (ask who they are) what you have and how to treat it the safest way. But you should also find out more about taking care of it yourself afterward... it may be that you need to repot into a faster draining gritty soil, keep it outside (for sure) until overnight temps go below 40 F. (they like and need some cold), and learn to water (and not overwater) properly, as well as how much light to give it, etc. Nursery people are not as likely to know that stuff as a local bonsai club/society would, so check into one of those if you can. Serissa can be a big pain to grow, as they often act sick for no good reason, and it's important to not overreact (e.g. by drowning it) if a few leaves fall, etc., but also to recognize problems like spider mite, etc.