Right now I wish there was a return label on this whole mommy thing- I know I will feel guilty feeling this way when I am not so sleep deprived, but right now I am just feeling beat up.
Do not feel guilty. It is so normal to feel that way! My LO was extremely fussy as a newborn (seems to be growing out of it somewhat) and at 10 weeks I had a moment. I was giving her a bath and I looked down at her and thought, "What have I done? I can't be someone's mother. I'm not prepared". Mind you, I was very sleep deprived at the time, waking every 90 minutes as you are now. I had to put my baby in her crib and walk outside my house and just cry. It was awful. I wanted to run away. Having a child is such a huge shock to the system. With hormones, sleep deprivation and depression it can be very hard. Having a fussy baby makes it even more difficult.
There is a light at the end of the tunnel. My LO is 15 weeks old and has improved immensely. 3 months really did seem to be the turning point for us. Some days are better than others, but there are more good days and it makes the tough days more bearable. Although I might have 3 days or broken sleep (going through 4 month wakefulness now, I believe), she will often give me a gift on the 4th day of sleeping 8 straight hours. Recharing really helps. Although she can still be fussy, she smiles and engages now and is much more fun to be around. I still have my days... but it gets better. Hang in there ladies.
My advice is to take it one day at a time. When you're in this stage, it feels like you will never, ever have a life again and it will be like this forever. Take heart that it won't.