Is it normal to have an upset stomach before every period after having children?

After having my last child (#3) 7 months ago and getting a tubal done, I've notice right before each of my periods I get the worst upset stomach. Mainly its gas, nausea, and just really bad stomach cramps like I ate bad food and I get so sick to the point were I want to take Pepto, now before this I've never had any kind of PMS symptoms except the normal ones such as slight bloating and the occasional cramp, but nothing like this. Could it be something from the tubal or after 3 kids my hormones have finally decided to change how I react to my periods? Does anyone else have these issues and any ways to make it a little bit more comfortable?