It sounds like you're having a bit of a difficult time, which must be rather hard when you've just returned to work anyway. I'm sorry for coming to this late, as you're probably already out with your clients.
In terms of your supply, if you keep expressing at the same intervals whilst you are separated then any formula she takes whilst away from you is unlikely to have a huge imact, unless it actually fills her up in the few hours before you are reunited. Supply is related to the amount of milk that's removed from the breast. So, if there's a disparity between what she is drinking and what you are able to pump, then the only way to try to get your supply to match her needs better is to increase the number of pumping sessions. I appreaciate that this might not be feasible whilst you are working, however. Generally to maintain supply it is advised that you pump as often as the baby would feed whilst you are separated. In a 12 week old baby a typical feeding pattern would be feeding every 2-3hrs (some feed slightly more often, others slightly less). So, in an 8hr day, assuming you fed before you left and immediately on return, that would suggest a minimum of 2 pumping sessions, but possibly 3. Often expressing is not as efficient at removing milk from the breast as a baby would be, so mums find they need to choose the higher number of pumping sessions in order to meet their baby's milk requirements.
There are ways you can try to increase your pumping output at each session. There are tips here and a video here} that is quite helpful (you'll need to watch it all). Anything that makes you feel relaxed or gooey and soppy about your baby may help during an expressing session. You can also try alternating breasts (if using a single pump) or starting hand expressing, then pumping, then hand expressing again.
In answer to your second question, a few things could be going on. Firstly, lots of mums say that around 3 months is a time where they notice that there baby has a more intense time of feeding and wants to feed more frequently, so it might be that this would be happening even if you weren't working. Secondly, it's really common for babies seaprated from mum by day to try to make up for that at night or when they are together by '[[http://www.kellymom.com/bf/normal/reverse-cycling.html reverse cycling}'. This isn;t necessarily just about nutition, but also about closeness and reconnecting with mum. Some mums encourage this as a way of maintaining their supply, and many find they get more rest and peace by keeping their baby close to them all evening and either bedsharing or using a 3-sided bedside cot at nighttime.
The tugging and sucking you describe could also be unrelated to your working. I've heard many mums say something similar about a baby of this age. Often it's because their baby has grown a bit longer, but perhaps the mum is still holding the baby in the same way as she did when they were a newborn and so they are not attaching to the breast (latching) in quite the most effective way possible. Often mums find that by tucking their baby's bottom more firmly into their side and moving their whole baby's body further away from the breast they are feeding from, so that the baby's head starts in mum's cleavage, can mean they tilt their head back further and latch on more effectively. Going back to basics, soch as making sure your whole baby's body is turned to face you (nose, navel and knees all in a straight line) and aiming your nipple at the roof of their mouth with their top lip just slidig over your nipple rather than poking the nipple in lik a bullseye can help. There are some pictures here that may help to remind you.
It must be really difficult if you need to work some evenings as well, as evenings are a classic time for young babies like yours to want to cluster feed. Most babies seem to grow out of it after the early months, but 14 weeks is still quite young yet.
Wanting to fall asleep on the breast is also really common and normal. A dummy is in fact a plastic imitation of a nipple, so they were invented for this very reason -because it is completely normal for babies to want to suckle. Babies seem to have a strong inbuilt need to suckle, and if you're concerned about your supply, then allowing your baby every opportunity to spend time at the breast is the best thing for maintaining this, whilst trying to ensure that her positioning is good so you are also comfortable. If you are able to spend some eveings just sitting on the sofa feeding whilst perhaps relaxing watching tv after a day at work, then lots of mums find going with the flow really helps. This phase doesn't last forever.
It sounds like you are doing your very best for your baby under difficult circumstances, needing to return to work whilst she's yet so young. There are bound to be things that are really hard, so try not to be too hard on yourself or expect too much too soon as you all adjust .