I feel trapped within myself

I just gave birth to my second child 4 weeks ago and I've been feeling kind of stressed and sad lately. I love my two girls with all the love I have on me bit sometimes I miss my old self. I know that sounds selfish but watching other 20 year olds partying going out having fun and being all care free makes me jealous sometimes. I know that it was my decision to have kids but I don't get why I feel so trapped. I no longer look forward in anything I barely have appetite to eat anything and lately I have been losing my patience with everything my one and a half year old does and that kills me. I tried talking to my boyfriend about my problems but he just sees it as me not wanting to play my role in being a mother and taking care of the home but it's not that it's just that through out the day I'm alone to raise two kids no connection to the outside world because I barely have friends the only connection I have is looking at other people live their lives through social media. I cry a lot get Constant headaches I get panicked and my heart races and I don't know what to make out of it. Am I just bring lazy and selfish am I sick or do I have a problem? Any advice?