I'm always tired (I have a 4 year old, work full-time with a long commute, so exhausted is my usual state!), so no one will notice much of a difference. In terms of energy day to day, if you don't have other children you need to be up with, take yourself to bed early. The exhaustion won't last forever. I felt much better by 10 weeks and great by 2nd tri, but in the early weeks, especially around 6-9 weeks, I was exhausted. I literally went to bed at like 7-8pm a lot of nights.
Buy yourself a few new things to wear so you are comfortable, but not in obvious maternity clothes. I couldn't fit in my usual clothes (trousers/jeans) by 6 weeks last time, so leggings, dresses, long flowy tunics over maternity trousers/jeans will help to make it a little less obvious that you are getting bigger/bloated, without looking like you are obviously pregnant. I also wear a lot of scarves normally, so I just drape them down the front so they cover up any bloat.
And frankly, we're just avoiding many social situations where it would be obvious that I wasn't drinking. I am never one to turn down a glass (or 3) of wine, and actually my husband joked yesterday that the first people who are going to work it out are our neighbors because our recycling bin is suddenly not bursting with empty wine bottles!
We got lucky that the next few months just happen to be really quiet - no weddings to go to, no events where there will be drinking, a lot of friends and family are busy, we're away or working a few weekends, so we literally won't really see many people until I'm past 12 weeks anyway. It just happened that way. Otherwise, if you need to disguise that you are obviously not drinking, if that would be a give away, I always either made myself a mixed drink with garnish and all, but it was really just soda water or tonic with a lime. Or I remember once last time I met a friend for brunch one day and I just got there early and ordered a virgin bloody mary, so it looked fancy, but really was just tomato juice with some hot sauce and celery in it. It also helps that the weather here is still cool so scarves and cardigans that wrap around me don't look out of place.
I've told one friend who I always tell, but we won't tell others til after our scan. I'll probably tell my mum around 8 weeks or so. I did last time and she's already moody enough about us having more kids (as in she isn't really keen on the idea because she found having me to be stressful, so she's always been a bit of a downer about making babies, even when I was pregnant with my first, never mind I'm an only child and they are her only grandchildren, but anyway!). Every time I talk to her she's like, 'I hope you aren't thinking of more kids soon!' (we're in our 30s, married, settled, highly educated, financially secure professionals, she just has a weird thing about us having kids because I think it was such a rough time in her life). So I want to head it off so she has a chance to get over it and not be too moody with me about it by the time we start telling more people and actually need her to be excited about it. I'll probably tell work about 12 weeks as well after our scan. I need to be planning ahead as my job is entirely grant funded and project based, so we need to plan what we'll do with our project while I'm off for a year and how we will organise the funding for it in terms of start days and such, so that's about the time we should start having those conversations. Fortunately, I work from home 2 days a week, so I just have to rally and look alive the other 3 days that I'm in the office.