What should I do?

My husband just told me his co-worker (female) invited him & his other co-workers for a bday dinner. I don't know how to feel about it because he didn't ask if I wanted to go. I had just told him about my friends bday party this Saturday I always try to include him & I felt bad that he didn't invite me. We rarely see each other because he works full time & goes to school & I work crazy retail hours.
Am I overreacting (pregnancy hormones) or should I be upset?