In that case why did some of my level 1 warlock spells turn into level 2 spells when I leveled up? really annoying because now I only have 1 level 1 spell to use in the level 1 spell slot....
Warlocks have a number of spell slots that aren't locked by level. You always cast spells at their highest level. In other words, at level 4 you can cast 3 spells per short rest.
