Ladies, do I need a bigger tampon size?

So I've used tampons for my last two periods and before that I had only used pads. I had no problems with using tampons the last two periods, they were great! But now (sorry if this is tmi!) the tampon slides out a little when I use the bathroom and so I leak a little if I continue to leave the tampon in, or if my flow is heavy, I leak out the side of the tampon. I use playtex sport regular tampons. Do I need a bigger size or something? Please help!
Ladies, do I need a bigger tampon size?
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