Hmmm, well you have a few options. I don’t think it is a matter of you “can’t” do it. It is a personal decision (with God) you have made to give up soda and coffee. If you feel that you need to adjust it because of your new job, I don’t think this is inherently “wrong.”
So you have a few options: you could try caffinated tea or other ways to get some caffeine in the morning to get going. That is one option. (Do not however, resort to caffeine pills or anything like that…that is not healthy, and I’m sure God wouldn’t want you to do something like that to your body).
You could just resort to giving up just soda (if that really is still a sacrifice for you). Or you could think of something else you could give up instead of the coffee…like maybe you could exchange coffee for chocolate. Or something else that makes sense for you.
Another option, is you could “do” something for your lenten sacrifice instead of giving up something. I tend to resort to this since I’ve had several health issues concerning food, so I’m already limited in what I can eat. So in general I give something…like I devote more time to prayer (say 10-15 min a day) or I go to daily mass more often. For example, this year since I know I need to be fair to my crazy schedule (as a pharmacy student and someone who works several hours a week), I told myself I’d double what I was already doing (at least 4 times a week).
So there are some thoughts

Good luck with your job!