Financing next property with Live in Duplex Rent / Payment

[Blake King]

Hello Everyone!

(tl;dr below)

I met with a Mortgage broker a few weeks ago, and came away very discouraged. 

I am currently in sales, with about 1.5 years of commission, getting close to the 2 year mark so it can qualify on my DTI. My current taxable income before i hit 2 years is only 30,000 / year, so there is not much i can qualify here north of Seattle. I did manage to buy a Duplex last June, with my dad as Cosigner, and a significant down payment. As i get closer to 2 years, i want to be ready to buy another property when my income is lend-able.

Here are the financing specifics. 

current mortgage $1700 / month.

Rent from unit A is $1200

We live in unit B, i think i could rent it for $1100 when i move out. 

The mortgage broker said we could not count that rental income towards my DTI when i plan to move out and rent, as it would have to be done before i moved. When i hit two years i am hoping to buy a property in the ballpark of 300k-400k+ and it is seeming impossible.

TL;DR - How can i qualify the rental income from the unit i live in, when i move out and try to buy another? Having this off will be crucial to getting financing. i have 0 other payments, no student loans, no car payments, no credit debt. 

Thank you for your help!!