My period was so short this month!!

My husband and I are TTC. I went off birth control in September and my periods have been regular and are about 4-6 days in length. Average is 5 days. This month we started using opks, so I know I ovulated on 1/7. I got my lh surge on 1/6. Well, I started my period two days ago. It was bright red and medium flow. Yesterday it was medium flow and then I haven’t had any today. My period was only 2 days... anyone have thoughts? Is it just an off month or could I still be pregnant? I tested on Monday and it was negative.