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As you are advised , best way to know if you are pregnant or not is wait till next period and if you miss it get a home pregnancy
If you are Rh negative
and your husband is positive , there could be a problem.But its unlikely as you already had three healthy children.
There are chances that you could be pregnant , but unlikely after tubal ligation
I advise you to wait till you miss your period and get tested.If the pain gets severe anytime , please visit ER immediately.