Sleeping worse than ever

My LO is 5.5 months and seems like she's sleeping worse than ever. Around 2 months she was sleeping from 8p-3:30awaking to eat (without fussing) and then sleeping until 7a. At 4 months she hit the sleep regression hard and began waking every couple hours. Now she is still waking constantly at night but is even harder to get back to sleep. She wakes crying and fussing. She still sleeps in our room and usually ends up in our bed because I just don't have the energy to go back and forth when she's waking and crying so often. She cut a tooth on Sunday so I'm not sure if it's the teething at this point or the sleep regression. Did anyone else have it last this long? Any tips? I work full time and I'm beginning to crash from sheer exhaustion.