Pelvic pain, got muscle relaxers, now constipation. Laxative?

There are several. There are several types of laxatives. Colase is simply a stool softener but may not be adequate for your purposes. The next level up is MiraLAX (polyethylene glycol) which works by drawing water into the bowel. Avoid the more harsh laxatives such as Ex-Lax and Dulcolax which can cause permanent damage to the bowel if over-used.
Maybe. Unusual for muscle relaxers to cause constipation. A laxative is certainly an option. Try an over the counter stool softener and increase your water intake.

Related Questions

Pelvic pain pills after muscle relaxers. Do they cause constipation?

Maybe. Depending on exactly what medication you are taking, narcotis used for pain have a tendency to cause constipation. Read more...
Maybe. Depends on the specific medication class. Certainly all opioids cause constipation, ie vicodin, percocet, oxycontin. Read more...