Alwasy getting a flat rear tire on my 14"inch folding bike I just bought my 14&quot; folding bike and I always getting a flat tire on the rear. It happened 4 times in a span of three days. 1st flat was with the stock inner tube, 2nd flat is with the new inner tube, 3rd same goes with 2nd. The mechanic advised me to change a bigger tire size from 1.75 to 2.25. 4th I thought it would solve the problem, rode longer than the old tire but still I got a flat tire. It's frustrating. I weigh 185lbs. Is that the reason why? But I've seen a lot of bikers who are bigger than me riding a 14 inch folding bike.
PS. They also added another rim tape.
There are a few possibilities:

The culprit is still stuck in the tire. Carefully check for any glass shards, pieces of wire, thorns etc.
Something is sticking out of the rim. Check if the rim tape is properly seated and covers the spoke holes completely.
You are using insufficient tire pressure and getting pinch flats (”snake bites”). Usually you’ll get two long-ish punctures on opposite sides of the tube. If you are riding on roads only and are on the heavy side it’s probably a good idea to go up to the maximum pressure the manufacturer recommends.
You are pinching the tube between rim and tire during installation. Or damaging the tube with tools. Install without tools if possible. Inflate to a very low pressure after installation and check if the tube is pinched anywhere by pushing the tire away from the rim and looking into the gap.
You are simply having lots of bad luck or there is a lot of debris on your roads in combination with a fragile tire. Get ”puncture proof” tires if you ride on roads with glass shards, thorns etc.

General advice: Install the tire with the label aligned to the valve stem. This way, after you’ve found where the puncture in the tube is you can check the corresponding area of the tire and rim.