What is "Menas Midayich"?
Rashi: It is your lot, based on your Midos - Midah k'Neged Midah. Radak - "Midayich" is like Midosecha. Like you measured, I measured to you. You forgot Me - I forgot you. You turned the back of your neck to Me, and not the face - I hid My face from you, and you were [for the enemy] to consume, and great afflictions befell you.
Radak: Perhaps Midah is used like feminine and masculine, like "Arba Pinosav" (Shemos 27:2 - feminine) and "Sha'ar ha'Panim" (Zecharyah 14:10 - masculine). Also Midah can be Midos or Midim in the plural
Why does it say "me'Iti"?
Radak: This is your lot and portion from My anger.
Malbim: [Your afflictions] are from Me; they are not chance. They are Midah k'Neged Midah, according to your sin.
How did they trust in Sheker?
Malbim: They descended to Egypt for help, and relied on [their] chariots, and did not turn to Hashem.