Pregnant and excersize. Help?

In November last year I found out I was pregnant, I then misscarried in December. It was a very emotional roller coaster. I stopped eating healthily and stopped excersising and I haven't been able to motivate myself back into the healthy lifestyle i was in. I've gained 5kgs in 5 months (which I think was an unnessisary 5kgs). I'm now 13 weeks pregnant and I want to be healthy and strong for the baby and for when I have to deliver. I think it's a mental thing for me also, eg. "gaining weight is gona happen anyway so don't worry about excersising"
Does anyone feel the same?
Does anyone have any tips or advise?
Help.