Congrats on your hard-earned results, chub39. Maybe it's time to change you're username now that you're a BUFF 150. (grin)
Take it slow and easy re raising your calories. If you're currently doing cardio, back off to no more than 2 or 3 HIIT-type sessions (20 minutes max).
Give it a few days to a week and watch the scales.
From there you you need to start adding in calories, as you've already surmised. My recommendation is that you add 100-125 calories to your PWO nutrition in the form of starchy carbs. Keep all other things the same. Give it a week. Then add another 100-125 calories once again in the form of starchy carbs to a second PWO meal. Starchy carbs are defined as brown rice, sweet potatoes, yams, oatmeal.
Make sure you're meeting your protein and healthy fat requirements; i.e., 1.5g x LBM for protein and .4 to .5g x LBM for fat. If you work out in the evening, you should be eating green veggies during the day and starchy carbs PWO.
From there, pick a good bulking program. I like Chad Waterbury's programs and Charles Staley's EDT for bulking.
That ought to give you a running start. Once again, congrats on the results.