I had mood swings before pg and a lot of people told me 'fish oil'. I had taken an over the counter fish oil from the store for years but had stopped after reading some conflicting things about some fish oils. In the interim I started leaning toward a nourishing traditional food approach so at that point my fish oil of choice was FCLO (fermented cod liver oil). However, I'm pretty sure I did not react well to FCLO--felt like my mood swings got WAY worse. When I stopped the FCLO, the mood swings got better. Anyway, I started taking 'regular' fish oil again (salmon oil from Vital Choice) and felt pretty good with that and then when trying to get pg I switched to Vital Choice's Krill Oil (a splurge) and I feel GREAT. I felt great in mood and it helped with non-mood related stuff as well I think. So anyway, I hear 'fish oil' a lot for mood things and I just wanted to throw out that Yes! I think that can work really well, but always check in with yourself and make sure the kind you're taking is working for you.
Other than nutritional type things (you could also try increasing your fatty acid consumption through food, salmon and walnuts and other things too) I would suggest sleep (can you fit in a nap? get to bed earlier), talking with sympathetic individuals, getting out for some sun and fresh air and long deep breaths for recharge in the moment. I can't imagine dealing with all the pg yuckies on top of raising a really little one--that's a lot of patience required! Maybe you could find a mothers helper to come lend a hand from time to time so you can focus on something for yourself? Also, taking some time out for yourself in the evening may help you regroup.
I went to see an acupuncturist about my nausea and fatigue and she inquired about my mood. Since my mood was fine I didn't ask about it but I'm assuming from her question, perhaps there's some mood-lifting acupuncture methods? Maybe look into that?
Also, I think it's really normal to have a wide range of emotions, even for a planned pg! We planned ours for YEARS but I've still caught myself thinking 'what the *#()#@ was I thinking?!' and 'how am I going to DO this' contrasted with really loving, calming, reaffirming thoughts. The scary thoughts usually pop up at night or in the middle of the night and I just try to breathe through them and tell myself it will all work out and I won't solve anything by freaking out over it a 3 am. Be gentle with yourself and realize that you can reaffirm yourself despite your fears.