should i or do i have a case to sue for three months wages ?

Of course you may sue. If you performed work for someone that they wanted or asked you to do, they are required to pay you for it. Under the labor laws (such as the Fair Labor Standards Act, or FLSA), an hourly employee must be paid for all hours they work, plus overtime when you work more than 40 hours in a week. (You are not paid when "on call" if not actually working.) And you must be paid at least minimum wage, which in CA was $11.00 per hour. And under the basic principals of contract law, if there was an agreement that you would work for someone for $X per hour, and you performed the work, they in turn are contractually obligated to pay as agreed (i.e. $X/hour for all hours worked). Furthermore, under the principal of "unjust enrichment," the law does not allow someone to accept services from you which they know or reasonably should have known you were doing only for pay without in fact paying you for them, since to allow them to accept paid services without paying is to "unjustly"--or unfairly and wrongfully--"enrich," or benefit, them. So there are three separate grounds to sue. 
There could be a lot of money at stake. Even if we ignore overtime, if you actually worked 40 hours per week, you'd be owed (at minimum wage) at least 40 x $11/hour or $440/week. For three months, that would be 12 weeks x $440/week or $5,280. And if you worked more hours than that, you'd also be entitled to overtime. To continue with this example, if you worked 40 regular and 20 overtime hours per seek, your weekly pay would have been at least $770/week, or $8,470 for 12 weeks or 3 months. And in some circumstances, you may be entitled to attorneys fees for a labor law violation. You may wish to consult with an attorney about bringing a lawsuit. Good luck.