That seems normal to me, 30 days can be a bit short for a holiday, but over 60 days or even 90 days and then again within a month has nothing to do with tourism, so it is a correct decision of the immigration officer.
Just get the proper visa for your purpose of stay and you don't have to wait.
Visa exempt is for tourists, and I think with 3 visits of a month and one visit of 3 months in about a year time it might be difficult to make an immigration officer believe you are a tourist, but you just might have some luck.