50 mg can absolutely affect your current state. It has been known to induce hypomania and mania, sometimes even when on Lamotrigine. You are on only 50 mg of Lamotrigine too, and the therapeutic dose typically is 100-200 mg at minimum (I was told), so there may not be enough "protection" from the hypomania/mania at this point since you are not being fully stabilized by Lamotrigine just yet.

I am Bipolar 1, and based on my history of mania and personal experience with these particular meds, I am extremely sensitive to SSRIs/Zoloft. In fact, I had a manic episode and a horrible mixed manic episode on 50 mg of Zoloft and 200 mg Lamotrigine. So it can definitely happen. However, everyone is different. Just trying to answer your question that yes, the medication can very well be causing this. Definitely talk to your pdoc sooner rather than later. Sorry you are going through this.