Tubes Are Tied, Baby Kicking Feel In The Abdomen. Had Heavy Periods. What Could It Be?

Hi, I'm a 49 year old woman. Still getting monthly menstrual cycles. I have two children, 18 and 16 years old and had my tubes tied right after my last child. During the past two months, I've been feeling what I can only describe as a baby kicking my abdomen. The only other times I've ever felt this was during pregnancies. It doesn't feel like gas and it just started recently. I haven't had a pregnancy test although I'm sexually active, but as mentioned, tubes are tied. What could this possibly be? I keep thinking it's a mass or tumor or even worms/parasites, but nothing else is affected in my health, other than my last two periods were heavier than usual. Thanks in advance for your kind help.