Yes, definitely check out the tenant survival guide. Whether the increase is legal depends on if the landlord’s property is exempt from rent control.
That said, nothing about this sounds especially fishy. Most lease agreements automatically become month-to-month after the initial term expires. No signatures needed. If the LL owns 4 or fewer rental units, then nothing really limits the amount of rent he can charge. You will often do well to ask for another long-term lease to lock in a price you’re comfortable with. Most LLs would prefer the security of a long-term tenant to a month-to-month arrangement anyway. Many lose 5-10% of their rental income to vacancy.
Best of luck.