Reward very low

[chenus1]

I have window 8.1 pro farming node, with total 690 TB harvesters ( my own farming without joining any pools). I did created all plots without joining any pools. The estimated reward is ~12 days, however, I did receive 2 XCH about 1 month for more than three months. Is it normal? I had my 8444 port open. What is the statics for me to get average reward? I feel discouraged for farming as it seams not a good investment for me...
Please help clarify and help me how to improve the rewards! thanks