Wow, I am exactly your size, 188cm, and I weight 80kg. I consider myself skinny. After a long tour through Africa (one year on a bike) I weighted 66kg and was very aware of the health problems. I am back on 75-85kg, it varies depending on the tours I do. With 10kg less, you should really aim at gaining weight.
My advise, as someone who knows how to gain/lose weight (from personal experience, as well ad having a girlfriend that is a personal trainer)
Running/Cycling/Cardio = BAD. Seriously, consider doing none of these for a while.
Weightlifting = Good.
More food = Most important.
Start counting calories. Aim at 4000-5000 a day. Milk + Bananas + Proteinpowder is a good way to supplement your food. Make a liter or so each day. Since you dont seem to mind getting also gains in non-muscle mass, add fast food, lots of fats or chocolate to your diet. When I am in between tours, I eat at least one block of chocolate each day, its easy 600 extra calories.
When I am on tour, I need 6000-10000 kalories a day, which is 40 chicken mcnuggets or 2,5 bigmacs around every 3 hours... so it could be worse than "just" trying to gain weight. I do up to 10 hours of cardio a day, and have to eat that just to stop losing weight.
A important tip for the beginning: Write everything down. Its easier to spot mistakes, skipped days, but also gained weight that way.
Mind that you will spend more money than before, because your calorie intake / food will be 2-4 times higher than before.
Sappoh: Seriously, Running and Weightgain/Muscle building = No. The runners tou know are probably fit and build muscles in the gym with resistance training, and they simply look like they have more muscles, because they are well defined and reduced their bodyfat percentage by doing cardio. But there are not muscular Marathon runners. Sprinters, yes, but not long distance. You also wont get strength increase from running.